BU-302: Series and Parallel Battery Configurations. DIY 72v ebike battery

How to Install Dual Batteries on an Ebike

If you have an ebike and have been wanting more range or speed, you might be wondering how to install dual batteries on your ebike. There are a couple of ways this can be done and some are more viable than others.

When connecting dual ebikes in series, you have to connect the positive of the first battery to the negative of the second battery. After that, connect the remaining free positive and negative connections to the ebike speed controller. All ebike batteries should have a BMS, and problems can arise when running 2 ebike batteries in series. This is because the MOSFETs in the BMS are not going to be rated for the full battery voltage of both packs. Under normal operation, this is not a problem as the voltage across the MOSFETs on both battery packs is close to zero. When one battery dies, however, its MOSFETs will switch into a high resistance state. When this happens, those MOSFETs will experience the voltage of the still working battery and the voltage of the dead cells in the dead battery. In most cases, this will overvolt the MOSFETs in the BMS of the dead battery.

When connecting dual ebike batteries in parallel, you have to connect the positive from the first battery to the positive of the second battery. After that, you can connect the speed controller to either battery. It’s important for the batteries to be at the same voltage before connecting them. If they are not, then a large amount of current will flow from the higher voltage battery to the lower voltage battery. Even if the batteries are at the same voltage when you connect them and everything seems to work fine, its not good to put two batteries of different capacities in parallel. This causes the batteries to be in an imbalanced state of discharge and makes it so the larger battery is always charging the smaller battery at an unpredictable rate. This puts extra strain on everything and reduces the life of the batteries. People usually don’t notice because there is still a net gain in capacity from adding the second battery, but it’s really reducing the overall life of the system.

In this article, we will go over how to install dual batteries on an ebike. We will also explain the pros and cons for each setup, and when to not do each one.

Installing Dual Batteries In Series

So, a lot of people are wanting to know if it’s possible to wire 2 36V ebike batteries in series to make a 72V battery. Wiring up two batteries to make a 72V setup is technically possible, but it is not recommended. The main concern is the Battery Management System (BMS) and what voltage its components are rated for. A BMS controls access to the battery via n-Channel MOSFETs, which are rated for a particular voltage that is some amount higher than the voltage they are used for. For example, the MOSFETs in a 36V BMS are generally rated for 45 volts.

The problem arises when one of the batteries in the series fails, causing the MOSFETs in the dead battery to be exposed to a voltage that exceeds their rating. This can lead to damage to the BMS in the dead battery and, in rare cases, even a fire. To avoid these issues, it’s important to take great care to ensure that neither battery dies.

Using a BMS is necessary as it provides a safety measure for lithium batteries, so bypassing one or both BMS to get around this problem is not a viable solution. However, if you take the necessary precautions and ensure that neither battery dies, it is possible to wire up two batteries to make a 72V setup.

It is possible to tie discharge gate control pins on each BMS together with a wire, but this is an advanced procedure that requires modifying both BMS. Another thing to consider is the voltage differential between two gate pins associated with 2 BMSs in series. There will more than likely be a dangerous difference between the two, so in addition to all the other work, isolation circuitry would have to be employed.

Consider The Rest Of The System

Watts equals volts times amps. If you have an ebike controller that is limited to 30 amps and you have a 48V battery, then how many watts is that?

36 Volts x 30 Amps = 1080 Watts

So, what happens if you double your system voltage by putting two 36V batteries in series?

72 Volts x 30 Amps = 2160 Watts

So, if the controller supports it, then you will get twice the power out of the controller. But only if you want twice the power. The thing about running a higher voltage on an ebike is that you can choose how much of that power to use. So, if you combine two batteries and adjust your power level to half of what it was before, you will have the same 1080 Watt limit at a higher running voltage.

But remember, Watts is Volts times Amps, which means that Amps is Watts divided by Volts. So let’s do the math to find out how many amps would be required to run a 72V load at 1080 Watts.

1080 Watts ÷ 72 Volts = 15 Amps

This means that you can get all the power you were used to while putting your batteries under half the stress as was required before. This will result in a much longer overall battery lifespan and will provide an excellent buffer against voltage sag.

Installing Dual Batteries In Parallel

It is possible to wire two ebike batteries in parallel to increase capacity and it is much safer and much more tolerant to error than wiring them in series, as it eliminates the risk of overvoltage damage to the BMS.

When wiring two ebike batteries in parallel, it is important to ensure that the batteries are of the same type, and capacity and that they are rated for the same voltage. This is because if one battery is larger than the other, it will more than likely have lower internal resistance and will provide more than its fair share of the load current.

This will lead to an imbalance in the system that will be quickly and unpredictably corrected by a rush of current from the larger battery to the smaller one on every discharge. This can damage both batteries and if the wiring between the two can’t support the higher currents, it could start a fire.

When doing this, you have to make sure that the positive and negative terminals of each battery must be connected to the same terminals on the other battery. Before connecting the two packs together both packs need to be at the same voltage, within.1v of each ideally. If this is not done correctly, it will cause a short circuit, which can cause burns and/or ruin one or both batteries.

Consider The Rest Of The System

When adding two batteries in parallel, whether they are properly matched or not, the rest of the system doesn’t know any different. It will see the same running voltage and power will be applied as normal. It is worth mentioning, however, that because there is another battery there to share the load, each battery will bear less of the load than it otherwise would have had it been the only battery in operation.

This helps to extend the life of the batteries and works against the face that if the batteries are mismatched, overall life is reduced. This situation ends up creating somewhat of a balance that produces an overall net-positive effect when adding batteries in parallel, even if they are mismatched. This is why many people swear by this method and say that it works perfectly.

Simple Way To Install Dual Batteries On An Ebike

The best way to use multiple batteries on an ebike is to put them in parallel. This is only truly viable if you have two matched batteries, though. If the batteries are not matched, the best thing you can do is use a switch to toggle between them. The problem is that switches that can handle that amount of current are often expensive and bulky. So, the simple solution is a manual one.

When your first battery dies, simply unplug it and plug the other battery in. All you have to do to make this possible is to run the wiring in the right places on your bike and put the connections in the most ideal spots for you to switch them.

Swapping over a cable into another port is a quick, painless procedure and it is the easiest, most effective, and safest way to install dual batteries on your ebike. The only downside is the fact that it is not automatic and requires the bike to stop for a moment. This is a more than worthy tradeoff, considering its low cost and simplicity.

There are also battery discharge combiner modules, but it is important to keep in mind that they often have relatively low current limits. For example, the first listing for the linked battery combiner specifically says to not use it with a non-geared motor. This is because without gears, starting from 0 uses quite a bit of power. Whereas the second one does not have that noted since it can handle higher amperage.

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Consider The Rest Of The System

This is the least invasive way to add dual batteries to an ebike in terms of system characteristics. This is because the batteries are not connected at the same time, so all the precocious and disclaimers above go out the window. In fact, because the batteries are totally isolated and never used together, you can even confidently mismatch different voltages, capacities, and even cell chemistries.

You could have an LFP pack for short runs as they have an extended cycle life and you could have an NMC pack for long range as they have the highest energy density. You could have a large, 48V pack for long runs and you could have a small, 72V back for short races on a track or other closed circuit. The possibilities are endless because the batteries are never connected at the same time. As long as your controller supports the voltage of whatever battery you plan on connecting to it, it will be fine.


Installing dual batteries on your ebike can be a great way to increase its range and speed. However, the method of connecting the batteries is crucial to ensure safe and reliable operation. Connecting the batteries in series involves connecting the positive of the first battery to the negative of the second battery, and then connecting the remaining connections to the speed controller. However, problems can arise if the batteries are not matched and one battery dies, which can overvolt the BMS in the dead battery.

On the other hand, connecting the batteries in parallel involves connecting the positive of the first battery to the positive of the second battery, and then connecting the speed controller to either battery. It’s important for the batteries to be at the same voltage before connecting them, and to avoid putting two batteries of different capacities in parallel as it can cause an imbalanced state of discharge and reduce the life of the system.

We hope this article contained everything you wanted to know about how to install dual batteries on your ebike, thanks for reading!

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BU-302: Series and Parallel Battery Configurations

Batteries achieve the desired operating voltage by connecting several cells in series; each cell adds its voltage potential to derive at the total terminal voltage. Parallel connection attains higher capacity by adding up the total ampere-hour (Ah).

Some packs may consist of a combination of series and parallel connections. Laptop batteries commonly have four 3.6V Li-ion cells in series to achieve a nominal voltage 14.4V and two in parallel to boost the capacity from 2,400mAh to 4,800mAh. Such a configuration is called 4s2p, meaning four cells in series and two in parallel. Insulating foil between the cells prevents the conductive metallic skin from causing an electrical short.

Most battery chemistries lend themselves to series and parallel connection. It is important to use the same battery type with equal voltage and capacity (Ah) and never to mix different makes and sizes. A weaker cell would cause an imbalance. This is especially critical in a series configuration because a battery is only as strong as the weakest link in the chain. An analogy is a chain in which the links represent the cells of a battery connected in series (Figure 1).

Figure 1: Comparing a battery with a chain. Chain links represent cells in series to increase voltage, doubling a link denotes parallel connection to boost current loading.

A weak cell may not fail immediately but will get exhausted more quickly than the strong ones when on a load. On charge, the low cell fills up before the strong ones because there is less to fill and it remains in over-charge longer than the others. On discharge, the weak cell empties first and gets hammered by the stronger brothers. Cells in multi-packs must be matched, especially when used under heavy loads. (See BU-803a: Cell Mismatch, Balancing).

Single Cell Applications

The single-cell configuration is the simplest battery pack; the cell does not need matching and the protection circuit on a small Li-ion cell can be kept simple. Typical examples are mobile phones and tablets with one 3.60V Li-ion cell. Other uses of a single cell are wall clocks, which typically use a 1.5V alkaline cell, wristwatches and memory backup, most of which are very low power applications.

The nominal cell voltage for a nickel-based battery is 1.2V, alkaline is 1.5V; silver-oxide is 1.6V and lead acid is 2.0V. Primary lithium batteries range between 3.0V and 3.9V. Li-ion is 3.6V; Li-phosphate is 3.2V and Li-titanate is 2.4V.

Li-manganese and other lithium-based systems often use cell voltages of 3.7V and higher. This has less to do with chemistry than promoting a higher watt-hour (Wh), which is made possible with a higher voltage. The argument goes that a low internal cell resistance keeps the voltage high under load. For operational purposes these cells go as 3.6V candidates. (See BU-303 Confusion with Voltages)

Series Connection

Portable equipment needing higher voltages use battery packs with two or more cells connected in series. Figure 2 shows a battery pack with four 3.6V Li-ion cells in series, also known as 4S, to produce 14.4V nominal. In comparison, a six-cell lead acid string with 2V/cell will generate 12V, and four alkaline with 1.5V/cell will give 6V.

If you need an odd voltage of, say, 9.50 volts, connect five lead acid, eight NiMH or NiCd, or three Li-ion in series. The end battery voltage does not need to be exact as long as it is higher than what the device specifies. A 12V supply might work in lieu of 9.50V. Most battery-operated devices can tolerate some over-voltage; the end-of-discharge voltage must be respected, however.

High voltage batteries keep the conductor size small. Cordless power tools run on 12V and 18V batteries; high-end models use 24V and 36V. Most e-bikes come with 36V Li-ion, some are 48V. The car industry wanted to increase the starter battery from 12V (14V) to 36V, better known as 42V, by placing 18 lead acid cells in series. Logistics of changing the electrical components and arcing problems on mechanical switches derailed the move.

Some mild hybrid cars run on 48V Li-ion and use DC-DC conversion to 12V for the electrical system. Starting the engine is often done by a separate 12V lead acid battery. Early hybrid cars ran on a 148V battery; electric vehicles are typically 450–500V. Such a battery needs more than 100 Li-ion cells connected in series.

High-voltage batteries require careful cell matching, especially when drawing heavy loads or when operating at cold temperatures. With multiple cells connected in a string, the possibility of one cell failing is real and this would cause a failure. To prevent this from happening, a solid state switch in some large packs bypasses the failing cell to allow continued current flow, albeit at a lower string voltage.

Cell matching is a challenge when replacing a faulty cell in an aging pack. A new cell has a higher capacity than the others, causing an imbalance. Welded construction adds to the complexity of the repair, and this is why battery packs are commonly replaced as a unit.

High-voltage batteries in electric vehicles, in which a full replacement would be prohibitive, divide the pack into modules, each consisting of a specific number of cells. If one cell fails, only the affected module is replaced. A slight imbalance might occur if the new module is fitted with new cells. (See BU-910: How to Repair a Battery Pack)

Figure 3 illustrates a battery pack in which “cell 3” produces only 2.8V instead of the full nominal 3.6V. With depressed operating voltage, this battery reaches the end-of-discharge point sooner than a normal pack. The voltage collapses and the device turns off with a “Low Battery” message.

Batteries in drones and remote controls for hobbyist requiring high load current often exhibit an unexpected voltage drop if one cell in a string is weak. Drawing maximum current stresses frail cells, leading to a possible crash. Reading the voltage after a charge does not identify this anomaly; examining the cell-balance or checking the capacity with a battery analyzer will.

Tapping into a Series String

There is a common practice to tap into the series string of a lead acid array to obtain a lower voltage. Heavy duty equipment running on a 24V battery bank may need a 12V supply for an auxiliary operation and this voltage is conveniently available at the half-way point.

Tapping is not recommended because it creates a cell imbalance as one side of the battery bank is loaded more than the other. Unless the disparity can be corrected by a special charger, the side effect is a shorter battery life. Here is why:

When charging an imbalanced lead acid battery bank with a regular charger, the undercharged section tends to develop sulfation as the cells never receive a full charge. The high voltage section of the battery that does not receive the extra load tends to get overcharged and this leads to corrosion and loss of water due to gassing. Please note that the charger charging the entire string looks at the average voltage and terminates the charge accordingly.

Tapping is also common on Li-ion and nickel-based batteries and the results are similar to lead acid: reduced cycle life. (See BU-803a: Cell Matching and Balancing) Newer devices use a DC-DC converter to deliver the correct voltage. Electric and hybrid vehicles, alternatively, use a separate low-voltage battery for the auxiliary system.

Parallel Connection

If higher currents are needed and larger cells are not available or do not fit the design constraint, one or more cells can be connected in parallel. Most battery chemistries allow parallel configurations with little side effect. Figure 4 illustrates four cells connected in parallel in a P4 arrangement. The nominal voltage of the illustrated pack remains at 3.60V, but the capacity (Ah) and runtime are increased fourfold.

A cell that develops high resistance or opens is less critical in a parallel circuit than in a series configuration, but a failing cell will reduce the total load capability. It’s like an engine only firing on three cylinders instead of on all four. An electrical short, on the other hand, is more serious as the faulty cell drains energy from the other cells, causing a fire hazard. Most so-called electrical shorts are mild and manifest themselves as elevated self-discharge.

A total short can occur through reverse polarization or dendrite growth. Large packs often include a fuse that disconnects the failing cell from the parallel circuit if it were to short. Figure 5 illustrates a parallel configuration with one faulty cell.

A weak cell will not affect the voltage but provide a low runtime due to reduced capacity. A shorted cell could cause excessive heat and become a fire hazard. On larger packs a fuse prevents high current by isolating the cell.

Series/parallel Connection

The series/parallel configuration shown in Figure 6 enables design flexibility and achieves the desired voltage and current ratings with a standard cell size. The total power is the sum of voltage times current; a 3.6V (nominal) cell multiplied by 3,400mAh produces 12.24Wh. Four 18650 Energy Cells of 3,400mAh each can be connected in series and parallel as shown to get 7.2V nominal and a total of 48.96Wh. A combination with 8 cells would produce 97.92Wh, the allowable limit for carry on an aircraft or shipped without Class 9 hazardous material. (See BU-704a: Shipping Lithium-based Batteries by Air) The slim cell allows flexible pack design but a protection circuit is needed.

Li-ion lends itself well to series/parallel configurations but the cells need monitoring to stay within voltage and current limits. Integrated circuits (ICs) for various cell combinations are available to supervise up to 13 Li-ion cells. Larger packs need custom circuits, and this applies to e-bike batteries, hybrid cars and the Tesla Model 85 that devours over 7000 18650 cells to make up the 90kWh pack.

Terminology to describe Series and Parallel Connection

The battery industry specifies the number of cells in series first, followed by the cells placed in parallel. An example is 2s2p. With Li-ion, the parallel strings are always made first; the completed parallel units are then placed in series. Li-ion is a voltage based system that lends itself well for parallel formation. Combining several cells into a parallel and then adding the units serially reduces complexity in terms of voltages control for pack protection.

Building series strings first and then placing them in in parallel may be more common with NiCd packs to satisfy the chemical shuttle mechanism that balances charge at the top of charge. “2s2p” is common; white papers have been issued that refer to 2p2s when a serial string is paralleled.

Safety devices in Series and Parallel Connection

Positive Temperature Coefficient Switches (PTC) and Charge Interrupt Devices (CID) protect the battery from overcurrent and excessive pressure. While recommended for safety in a smaller 2- or 3-cell pack with serial and parallel configuration, these protection devices are often being omitted in larger multi-cell batteries, such as those for power tool. The PTC and CID work as expected to switch of the cell on excessive current and internal cell pressure; however the shutdown occurs in cascade format. While some cells may go offline early, the load current causes excess current on the remaining cells. Such overload condition could lead to a thermal runaway before the remaining safety devices activate.

Some cells have built-in PCT and CID; these protection devices can also be added retroactively. The design engineer must be aware than any safety device is subject to failure. In addition, the PTC induces a small internal resistance that reduces the load current. (See also BU-304b: Making Lithium-ion Safe)

Simple Guidelines for Using Household Primary Batteries

  • Keep the battery contacts clean. A four-cell configuration has eight contacts and each contact adds resistance (cell to holder and holder to next cell).
  • Never mix batteries; replace all cells when weak. The overall performance is only as good as the weakest link in the chain.
  • Observe polarity. A reversed cell subtracts rather than adds to the cell voltage.
  • Remove batteries from the equipment when no longer in use to prevent leakage and corrosion. This is especially important with zinc-carbon primary cells.
  • Do not store loose cells in a metal box. Place individual cells in small plastic bags to prevent an electrical short. Do not carry loose cells in your s.
  • Keep batteries away from small children. In addition to being a choking hazard, the current-flow of the battery can ulcerate the stomach wall if swallowed. The battery can also rupture and cause poisoning. (See BU-703: Health Concerns with Batteries)
  • Do not recharge non-rechargeable batteries; hydrogen buildup can lead to an explosion. Perform experimental charging only under supervision.

Simple Guidelines for Using Secondary Batteries

  • Observe polarity when charging a secondary cell. Reversed polarity can cause an electrical short, leading to a hazardous condition.
  • Remove fully charged batteries from the charger. A consumer charger may not apply the correct trickle charge when fully charged and the cell can overheat.
  • Charge only at room temperature.


[1] Courtesy of Cadex

The material on Battery University is based on the indispensable new 4th edition of “Batteries in a Portable World. A Handbook on Rechargeable Batteries for Non-Engineers” which is available for order through Amazon.com.

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I’m having trouble and was hoping you could help me. I have (2) JY Power HP-40s in my vehicle. They’re connected together using aluminum bars At resting the voltage on both is 13 volts (approximately). Once I start the vehicle 1 jumps immediately to 14.7 (approximately) and the other stays at resting. When I turn the stereo system on, I can watch the battery monitor (wired in to each battery) on the battery at 14.7 fluctuate from pulling power. The battery that sits at resting does not fluctuate. I’ve double and triple checked everything and I’m at a huge stand still. Please help. Thanks in advance.

As u have shown the battery connection but would like to ask you that if we want to make a circuit for 6v 3A solar

hai sir, i have a doubt about 18650 3.7v batteries in 7 x 3 position One side both positive and negative two line short.another side oppsite line two sides shorted, WHY? pls answer me sir thankyou

A circuit consists of 2 series connected batteries; the positive terminals of the batteries are connected to each other; the negative terminals connects the rest of the circuit. One battery is rated 100V and the other, 350V. This series connection is further connected to a single series load resistor. After connecting the load resistor, a potential difference of 228,7 V was observed across the load. A current of 15,25 A was measured. Determine the internal resistance values of the batteries if the volt drop in the 100V cell is 10.7V.

In Figure 6 above, if I have a NiCd cell batteries, which configuration is better, series all cells then parallel or parallel both then connect in series. Meaning in between cell there is no jumper to parallel two cell or batt. It’s like 2s then parallel as compared to 2p then series it.

The nominal cell voltage for a nickel-based Hi. I had the understanding earlier on that Li-ion are of many types including Li-posphate, Li-cobalt etc but this statement in the sixth paragraph seems to suggest that Li-ion isn’t a name for a group of batteries but is a specific battery chemistry “Primary lithium batteries range between 3.0V and 3.9V. Li-ion is 3.6V; Li-phosphate is 3.2V and Li-titanate is 2.4V.”

How48V,20AH lead acid battery can replace 60V,24AH LiFePO4 battery.

The nomenclature proposed above is not optimal. A better system is to place the first connection first, and the second connection second. For example: 4P16S is a pack such that cells are connected in groups of 4 in parallel, and 16 of those groups are connected in series. 16S4P is a pack such that cells are connected in groups of 16 in series, and 4 of those groups are connected in parallel.

Also, using an example of 4S4P is ambiguous. It would be better to use unequal values of S and P to clearly illustrate the point.

Looking at all this explanation I gained more knowledge and skills and experience how to connect my solar to a battery.

OK, this new format looks better. Will we be able to see the Комментарии и мнения владельцев from 2019-2021, please? Regards,

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Does single battery (e.g, LA, SLA, L-ion) better or multiple battery (in parallel) with same capacity (same AH) is better?

The free Android app “Battery Package Calculator” can help you calculate the parameters of battery packets.(up to 9999s 9999p) 🙂 https://play.google.com/store/apps/details?ID=pl.freshdata.batterypackagecalculator

I want to make a battery with 26650,500mah. I need 14.8v. How would I make a 4s 2p. I see the drawing for the 2s 2p. But you can say I am slow. Thank You for your help and time

how to best connection in power bank (Series Connection cell or Parallel Connection cell) Kindly write easy answer!

i want to 60 v 25 Ah battery pack by using 3.7 v 2.2 A lithium ion cells. how can i connect them to get better efficiency. is their any better way to connect them. i mean S ans P connection tricks

For an electric vehicle, I am looking at Nissan Leaf Gen 2 batteries. I am planning to use 48 Leaf modules at 8v and 66 ah. If I put the all in series, I will get 384v and 66 ah, I think. If I want more current, I go with 45 modules is series and 3 in parallel, do I get 360v and 198 ah or do I lose something along the way? John

I have a LiitoKala Lii-402 battery charger. The input is labeled 5V2A. How is this thing able to charge 4 3.7V Li-ion batteries in just a few hours? I purchased a BMS charger that wants something like 15V input to charge the same 4 batteries.

Hi Guys and Girls Could someone clarify for me the best configuration for an 18 x 48100ah Shoto Lithium Ion Battery Setup please? 3 Cabinets each with 6 units is what we’re looking at. Are there any suggestions regarding the monitoring softwares? Any extra Inforation would be highly appreciated. THANKS!

I have 4 3.2v 18650 batteries connected in series to power a 12v motor. Can I make a second 6v output from 2 of those 4 batteries and power both the motor off the 12v and say an Arduino off the 6v simultaneously?

Dear Sir need your guidance for sourcing of simultaneous charging and discharging controlling device for battery in electric vehicle Regards C.A.Nemade

Dear Sir Thanks for your Quick response and useful information Surely with your information I can able to take a step forward towards green energy I will surely disturb you If any further information is required. Regards C.A.Nemade

@ CA Popular 50A 12V / 24V / 36V / 48V MPPT Solar Charge Controller.-Foshan Top One Power Technology Co., Ltd. https://oneinverter.en.made-in-china.com/product/XyAELYzcYeVU/China-Popular-50A-12V-24V-36V-48V-MPPT-Solar-Charge-Controller.html 60 AMP Solar MPPT Charge Controllers for LiFePO4 Battery.-Wenzhou Xihe Electric Co., Ltd. https://xihe-solar.en.made-in-china.com/product/BSKELQWwMNhv/China-60-AMP-Solar-MPPT-Charge-Controllers-for-LiFePO4-Battery.html Search Made in China https://www.made-in-china.com /productdirectory.do?word=48V,30ampMPPTchargecontrollersubaction=huntstyle=bmode=andcode=0comProvince=nolimitorder=0isOpenCorrection=1 These are 2 of Chians biggest solar gear manufactuerers. Huge is sizebut still supply a 1 only quanties, as opposed to others who need FCL

Dear Sir I am working on the project of @ 1000 km running of vehicle with single charge pls let me know the commercial availability of 48 V, 30 amp MPPT charge controller for combination of Lithium iron Batteries/Life4 Batteries and Generator/solar combination Regards C.A.Nemade

I have a selection of 18650 cells all around 2100ah I want to make a pack at 12 volts at 10000ah for my scooter project my question is how many cells and in what configuration 3s means a nominal 10 volts so i am thinking going 4s is a better option so how many for a 3s 10000ah and how many for a 4s 10000ah

@ Dwight here are some charger manufacturers drop them aline about batteries https://danlcharger.en.made-in-china.com/product/lvCnLHgjYzRE/China-84-Volts-14-AMPS-Smart-Battery-Charger-1500W-Suit-for-Li-ion-and-LiFePO4-Battery-Types.html for a better quality suit in-built app https://danlcharger.en.made-in-china.com/product/YBNJxahdvLUQ/China-Waterproof-Battery-Charger-72V-15A-Worldwide-110-230VAC-with-Pfc.html cheers robb

Hello I have connected 5 numbers of 3.7 V, 3400mAh 18650 batteries in parallel to get 17000 mAh battery capacity. I’m measuring more than 10 A from the output of parallelly connected batteries. I need to know is that normal? Thank you for your reply.

Thanks for the response and I do not have any heave draw only a new Samsung inverter fridge. cooking with Gas and no Aircon or heaters needed only some power tools like grinders and small drill. mainly use for lights TV internet ans cable. I am creating a sample system to run TV, Internet, Cable TV and maybe microwave and toaster. I will start with 4 (maybe 6) Trojan 8V 170AH each from Golf Carts, set up as 2S groups then 2P to get 16V and 340AH. and maybe about 300 Watt Mono PV. then I will increase the batteries and the PV step by step until I get the best performance. I have a 3000/6000 Watt inverter to start. Step 2 will be 3S groups to get 24V then 3P to get 510 AH. will see. Thanks for your help good advice

@ Ceasar You dont actually say the max draw/demand. Rule of thumb double it !12V is good forrunning a couple of leds and a phone chargerbut if you want to be able to boil the billy in the morning you will want 6x800AH in 2 banks. I know as I was sold a12V sys years ago Disadvantages of lowvoltagestorage 1. enormous cables 90mm sq 2, 20:1 transformer windings =20Amp in gives less than 1 amp out 3. loss of conversion during charging and huge heat build up Suggest using 48V min even then look @ 420AH PoV expensive but last years verycommon and proven AVOID car batteries they are woftam (WASTE OF TIME AND FUXXXING MONEY) Also suggest a split sys,,get a 2nd Hand roof top upgrade with Grid tie in and use this as you DAYSHIFT Freezer,and high draw 240V.Build a skeleton 48Vsys for night shift Hope this helps @Robert You have the perfect WOFTAM, and a perfect recipe for failure and heartbreak Tell us a bit more about this common bus. it sounds more than the negative rail. one Band aide approach would be to have each battery with its own dedicated charging system and standalone discharge system Might look like Dr Who and the inside of the T.A.R.D.I.S. but it might just work Many Public Utilities cast out 2nd hand batteries once they reach 3 years oldbut they still have a 8/10 years ahead.this is a cheap option if the PRICE is RIGHT i.e., below 30% of new price robbo

I have several batteries in a bank, all different producing 12 volts. They are different ages and amp hour rated. If I take each battery to a common buss, will that cure the problems described with multiple batteries in parallel

Hi, I am building a solar system for my home and I wonder what will be the best way to obtain the most efficient system. I use many home appliances but initially I only have some basic ones like digital Samsung fridge, toaster microwave TV internet and cable (No heater or air conditioner). so If I set my batteries in series I will only increase the voltage but I think I will be much better to maintain the 12 volts and increase the Watts Hour by setting all in parallel that way I can maintain better use of the power. Am I correct with my assumption. Appreciate your help By the way my batteries are Trojan Deep cycle at 170WH Thanks a lot Cesar

Hi, I am building a solar system for my home and I wonder what will be the best way to obtain the most efficient system. I use many home appliances but initially I only have some basic ones like digital Samsung fridge, toaster microwave TV internet and cable (No heater or air conditioner). so If I set my batteries in series I will only increase the voltage but I think I will be much better to maintain the 12 volts and increase the Watts Hour by setting all in parallel that way I can maintain better use of the power. Am I correct with my assumption. Appreciate your help By the way my batteries are Trojan Deep cycle at 170WH Thanks a lot Cesar

long old thread. but one recurring question in led acid batteries regular flooded,deep cycle type. when using multiple they need to be same age,capacity and type for best results. series to increase voltage parallel for capacity. and more than 4 batteries theirs better ways than just for example 3x 12 series then 3 in series joined parallel than just and. search hooking up many 6 or 12 v batteries simple wiring change keeps batteries balanced. and banks of flooded cells need balancing every so often. lithium cells especially large amounts need a bms system and a way to fuse remember too lead acid 50% max lithium 70% usage and read more than 1 article

ANTIQUE ELECTRIC CAR I own a 1919 Milburn Electric car and would like to purchase lithium LIFePO4 batteries instead of the using the original lead acid batteries. The motor is a 76 volt 33amp DC GE motor from the era. The original system voltage was 84 volts (42 cells in 2 modules or 21 cells each) The manual controller with 12 brass contact fingers is organized as follows : “gear” 1 slowest speed, wheels beginning to turn, most ‘torque’ the motor is energized at 42 volts with the 2 modules in parallel and a resistor in place “Gear” 2 slightly faster and ‘torque’ still required to gain speed The motor is energized at 42 volts with the 2 modules in parallel and less resistance “Gear” 3 medium speed The motor is energized at 84 voltswith the 2 modules in series and even less resistance “Gear” 4 high speed least amount of ‘torque’ The motor is energized at 84 volts with the 2 modules in series and no resistors In “off” mode the lead acid cells were placed in series and the charger provided 84 volts. I have been talking to a lithium cell supplier who is willing to supply sufficient LIFePO4 120amp cells in 2 seperate and equal modules to provide nominally 42 volts each and a BMS for each These modules are recommended to be wired in series only for 84 volts and that they stay that way He does not recommend that they be connected alternately in parallel for 42 volts 240 amps. I am assuming that there is a concern that the 2 lithium ion modules will become out of balance with each other and risk fire and explosion A consistent 84 volt system will not work in this car Any suggestions that would lead to successful usage of lithium cells in 2 equal but separate 42 volt modules? Thank you

Hello All. I have 14 batteries 1.2V 4000mAh NiMh connected in series to get 16.8V pack. the pack has one PCB which i think to protect the batteries during the charging and usage. is there ready made similar PCB as mine is damaged and need to replace it. any advise on best way to overcome this.

Hello I have a battery/inverter set up in my garage comprising the following items. 1) One 5kVA RCT-axpert inverter, 48 VDC input, 220 VAC out. 2) 16 X 105 A/H, 12V Enertec Deep Cycle silver calcium batteries. Configured in 4 parallel banks of 4 batteries in series. These were installed about 3 years ago. This morning, I noticed a strong pungent smell in the garage area and found that one of the battery bank string was extremely hot which prompted me to disconnect it immediately. I suspect that one batteries in the hot bank could have developed an internal short. The batteries are constantly on maintenance.trickle charge, as provided by the inverter. Could you provide an opinion concerning this overheating incident. Thank you

do batteries (ie 12 v) have to be the same CCA when used in parallel for instance using a 500 CCA battery with a 875 CCA battery?

I have 6 (18650) li-ion batteries that i want to use for lead acid replacement for my motorcycle. Can i connect 3in Series and 3 in Parallel to achieve 14.4V ? How do i connect the 3inSeries with 3in Parallel onto each other and how to use a BMS for this configuration?My plan is to use this lithium pack to keep a pack of 6 supercapacitors always charged

Has anyone tried out a hydralight fuel cell? salt and water powered battery? Wondering if they would make a good solution for setting them up with many cells to power a house in a no power post hurricane emergency situation. Also wondering if anyone has tested them side by side with a normal d-sized 1.5 volt flashlight battery to see which lasts longer.

I plan to use two 12V 100aH batteries connected in series to create a 24V 100aH battery bank to power a 24V inverter. The bank will be charged by a 24V solar charge controller. 1. Do both batteries in the series configuration discharge at the same rate? Or does the upper battery discharge first and then the lower battery? 2. Will the 24V charge controller charge both batteries back up to their full charge? Or do I need to have two separate 12V controllers, one on each battery, in order to get both fully charged?

Can you reduce DC Ampere using resistors? serial or parallel. eg. (12V 11Ah DC) Resistor (OUTPUT 12V 1AhDC)

Hii, I have 24V battery system Two lithium-ion batteries connected in series connected to a Smart charger and inverter system. The batteries have a BMS of their own whose data can be accessed through Bluetooth. There are some DC loads on the battery system running on 24V. Now I charged both the batteries(in series) till 100% ( checked from BMS of both of them) and then started discharging the system. Today when I checked, one of the batteries were at 68% and another one at 94%. Both had the same discharging current and voltage as per BMS. So my question is what could be the reason behind unequal discharge. Both the batteries are new, same brand, same capacity. has anyone seen similar cases before.

I have a main circuit board in a machine that over a year or two eventually drains a 3.6v lithium AA size down to 1.4V. This battery has a wire soldered at each end which is then soldered to two points on the circuit board and is used to maintain data when the machine is shut down so it is there upon startup. I would like to use a parallel 4 battery holder that connects by soldering directly to the main board in place of the single battery and that the batteries can be removed from individually and easily without having to deal with soldering. My reason for this is that if the battery voltage drops down to the point that the machine no longer retains data then it takes about a half hour to reprogram the machine after changing (unsoldering and resoldering) the battery. I am hoping that by having multiple batteries in parallel they can be removed one at a time and be replaced without worrying about loss of data since it is still providing enough voltage. My concern is what I don’t know, which is if there are any adverse effects of having more than one battery even if in parallel. The battery I will use four or at least more than one if there are no problems is SAFT LS14500 Size AA 3.6V 2600mAh Primary Lithium (Li-SOCl2) Battery. This is the same type of battery that is wired singly to the circuit board now. I appreciate the help of those that are much more knowledgeable about this than me.

Hello, Could you please offer some advice. I’d like to know if there is a single cell battery that would be equivalent in size and voltage to a series stack-up of 4x AG3. I’d much prefer a single cell rather than fussing with four tiny batteries. Thank you.

@ Karl Series is the only way to charge batteries over an extended period. I have tried all sorts of ways to charge 12V batteries in parallel and long story short it is a waste of time. Often one battery is dead flat and others fully charged and are drawn down to the lowest voltage If you have GOOD batteries hook them in series and buy a new inverter of that voltage I did have a 6kw 12 V inverter (transformer type) running of 6x800Ah 2vPoe Batteries it worked well and could boil an electric jug in the morning Go series Robbo

I have a homemade solar setup. I use 4 identical 12 volt deep cycle marine batteries in parallel to power the inverter. I want to add capacity. I understand that it is important to use the same type of battery. Can I safely add 2 more batteries? Can I add 4 more? Is there a limit to how many batteries I can safely wire in parallel? Thank you in advance for your help.

@ Theo I have a mobility scooter powered with 3 AGM batteries 12v 28 ah, I can do only 10 to 12 Km. I live in a hilly suburb, if I want more distance and be prepared to buy an additional 3 batteries, of say 80 ah each so when I run out of power I can switch to the other bank. Could you please give me some advice how to connect those aditional batteries to get the required 70a for my scooter controller and have more distance I require to visit my local shopping centre, I don’t need speed just the wire connection of the 3 batteries to get the most ah. Hello Theo the math says it all, Your scooter draws 70 amp and you batteries supplies a total of 84 a/h, or just over one hour @ peak. Installing 3 x 80a/h would supply 240a/h or nearly 3 times the capacity and distance. If you install a second sett of batteries you would need a charging splittter as used in 4WD with twin batteries and a battery switch for A B banks (it gets complicated ) so stick with the new80a/h batteries

How do I get that information I ask for in my recent email of April 27 2018? Thank you, Theo Veeren veerent@bigpond.com

Hello to whoever reads, I need a low self-discharge battery (Lithium Thionyl Chloride) to power a microcontroller (somewhat like Arduino). It can handle 3.9. 12V and needs about 1800mA current in pulses. The Li-SOCl2 batteries I’ve been looking at is at 3.6V with 35000mAh capacity and can give a maximum continuous current of 450mA. If I put 2 of these batteries in parallel would I get twice the maximum continuous current (900mA) as the capacity also becomes twice the size? Sorry if this is a stupid question, but i’d rather find out here than to spend a bunch of money and realize it doesn’t work 😉 Thanks in advance, Michael

Hi.Sir/Madam I have a mobility scooter powered with 3 AGM batteries 12v 28 ah, I can do only 10 to 12 Km. I live in a hilly suburb, if I want more distance and be prepared to buy an additional 3 batteries, of say 80 ah each so when I run out of power I can switch to the other bank. Could you please give me some advice how to connect those aditional batteries to get the required 70a for my scooter controller and have more distance I require to visit my local shopping centre, I don’t need speed just the wire connection of the 3 batteries to get the most ah. Thank you. Theo,

For the Series/Parallel Connection, I don’t think the math adds up. If Figure 6 has 2 cells in series and its voltage doubles, and 2 series connections in parallel so its amperage doubles, then how does the Energy of four cells come out to 12.24 Wh? By my math: 3.6V 2 cells = 7.2 V; 3400mAh 2 = 6800 mAh; Power = Voltage Current = 7.2V 6800mAh = 48.96Wh

Hi Lior 10 x12Vdc = 120VDC @100A 12000W which is a good overnight storage to run a small house and one/two freezers. about the same size as a small Tesla battery It wont store enough for high load AC or huge heaters but but will run them for a few hours as needed U should still be able to boil the kettle in the morning Look on the web for an inverter 120VDC to 110/220V 5KVa or better and hook 20 x 300w @36V to give 5kw charge @150VDC to your inverter. Go series NOT 12V parallel Rule of thumb is panels should have a voltage about 25% above the battery bank voltage. Battery capacity is normal 2.5 /4.0 times the rated output of cells Solar is a necessity batteries are a luxury Batteries cost the money more so than panels PS if U dont want the batteries send them here, plenty of panels batteries hard to find and expensive still robbo

@ djay wrote: I need your help. I have 8, 6 volts, 450 amps battery. I need to get 48 volts and 450 amps or 950 amps. please help me with the wiring. Hi Djay its simple maths 8 batteries @ 6Vdc =48 Vdc connected in series positive to negative Wire sizes should be proportioned according to load 90sqm cables or (super duty welding leads would suffice @ 450A and doubled for 900amps You 8s2p or another 8 batteries to get 900A. What is the end use. the batteries would only have an intermittent discharge before overheating.~5/10% on cycle 90/95off cycle Use tinned welding cable that is soft and pliable, with professional crimps or soldered ends. Apply silicone grease to poles and conducting surfaces of lugs. Tension to recommended torque and check often, as they “hum” of this high discharge rate will shake and vibrate leads loosening the bolts/lugs. Thats a lot of power and if needed continuously a1200A Lincoln Sub Arc welder feeding from a 125A 415V Nelson Studs are spot welded onto bridge deck beams using a pulse welder with programmable amps and time and produce 2000amps Oddly they have 1 x 90sqmm positive lead and 4 x 90sqmm earth leads. the whole machine runs red hot and the leads are often seen smoking They use big rivet looking studs to 25mm dia in a gun with a cermic ring that holds the instant arc and molten metal in place drop the stud end into this molten bath until it solidifies Takes about 5 seconds as opposed to 6 x 4.00mm welding rods to give the same fillet size Gutsy machines but need a 250A 415V feed and or stand alone transformer

Hello I have a home solar system and I have two solar panels of 300W and my system is 24V. In addition I have 10 batteries of 12V and 100A each battery. I wanted to ask how to connect my panels to MPPT which means plug them into 36V or 72V? I want to use most of the electricity at night Thank you

I need your help. I have 8, 6 volts, 450 amps battery. I need to get 48 volts and 450 amps or 950 amps. please help me with the wiring.

@faizan Go to ebay there are dozens available for under 20US Here is one that may be veery useful as it is bare bones (you can easily see how it works and get an understanding) Also included are a single 18650 battery holder, a USB lead, and a phone charger lead. These alone would cost more to buy at the corner store if sold seperate Chimole 3.5W 5V Solar Panel Charging For 18650 Rechargeable BatterySolar Cell power bank Portable solar charger for Smart watch https://www.aliexpress.com/item/3-5W-5V-Solar-Panel-Charging-For-18650-Rechargeable-Battery-Solar-Cell-power-bank-Portable/32812373464.html?src=googlealbslr=225178492isdl=yaff_short_key=UneMJZVf&source;=src=googlealbch=shoppingacnt=494-037-6276isdl=yalbcp=1001718710albag=52375743834&slnk;=trgt=349475913279&plac;=crea=en32812373464netw=gdevice=c&mtctp;=gclid=EAIaIQobChMIzNSg7bK42QIVxwgqCh1WvwTgEAQYASABEgK0WPD_BwE It isalso available for under12.00 from https://www.banggood.com/3_5W-5V-130165mm-Solar-Panels-Charge-With-18650-Battery-Case-p-1167475.html?gmcCountry=AUcurrency=AUDcreateTmp=1utm_source=googleshoppingutm_medium=cpc_elcutm_content=zouzouutm_campaign=pla-au-ele-acs-dk-pcgclid=EAIaIQobChMIvMTPqLu42QIVV4C9Ch36zwF_EAQYASABEgKOv_D_BwEcur_warehouse=CN You can still tell your freinds you put it together The other option is to get some chips 7809, op amps,comparator chip,a timer, make a circuit board,install resistors and caps,solder on the headers, make the boxes and viola. 6monts later after hundreds of hours tinkering you either have something that works or a load of shite that ends up in the bin! Thats life. itsuptuyu. Remember, the poor man pays twice Cheers robbo

Hi! I had a small 9V solar system with a battery bank. I am using two 18650 batteries in series and they are being charged by solar panel and also gives back up power to my device which needs 6V 110mA atleast. But, after couple of hours of running second battery goes dead while first battery remains ok. and also solar panel does not produce enough voltage either where as it should be producing. what could be the problem? can anyone tell me? batteries can last about one and half day on full charge but they just gone bad. infact second one gone bad totally then the first one. Please help me

@Yujin An Per my last comment, I left out charge time details. Technically you might be able to charge 28 coin cells faster than a larger single cell, but at a cost of complexity and balancing issues (don’t expect it to last long as a power pack). Furthermore, 28 coin cells would be like 90cm x 5.8cm, whereas an 18650 is 18mm x 65mm and a 26650 is the same length but 26mm wide. I think this is about the best you can do, and it’s my recommendation to either use 18650 or 26650 cells, but make sure your gauge wire can handle the amps without getting hot: 26650 Specs: 3.7v @ 5.2 Ah = 19.98wH 5v @ 3 Amps (assuming discharge of ~50%) = ~40 minute charge 18650 Specs: 3.7v @ 3.0 Ah = 11 wH 5v @ 3 Amps (assuming discharge of ~50%) = ~23 minute charge Please note that actual charge time may vary, but this is an estimate based on capacity. Hope that helps and send you on the right direction. Thanks

@Yujin An I guess my last response was lost or something. I’ll keep it simple though. you might want to consider using 26650 cells instead. it be smaller than 28 coin cells and way less complicated. 1x would offer 3.7v at ~5Ah already. Not an endorsement, but I’d recommend EBL brand for the price and reliability. I’d imagine it cost less too, there’s no parallel/series charge issues and would require no BMS technically, etc. Best of luck!

I have three batteries use in my 4 wheel robot.I have 4 dc 200 rpm 12v motor. and I connect 6v 4.5 ah two batteries in series connect ed and it’s parallel connect one 12 v 1.3 battery. when switch on then my robot is not a full running. it’s torque and speed both very less. I don’t know what is reason. plyz reply me for this solution. tq

really helpful article! Can u help me. I’m student in mechanics. so I don’t know well about the battery and else things. I have some question for u. I want to charge lithium ion battery pack (28 coin cells of 3.5Ah, 3.7V and configuration is 471 = TWL ) than how to cinfigurate the circuits of charging. I have to charge in 30 minutes. 🙁

Great article, there’s a lot of information out there that’s just confusion because they don’t read in plain English. The illustrations/diagrams were also very helpful to visualize the parallel vs series circuits and helps to visualize and realize the benefits of a hybrid system. I just wanted to leave a comment and say I wish I came across more information written this way and I’ll use this article to educate my son. Thanks a bunch! Micheal

Daniel wrote: I have 4x 12v AGM battery connected in series for a total of 48V. I would like to be able to switch off the circuit using a 12V 30A switch. How much voltage would be accross that switch in the off/on position if I was to install it between the first battery and second battery. ? Is it possible at all? Daniel Volts can be cosidered as pressure (in a hydraulic system) a 12 v hasless insulation than a 48V switch or solenoid have a look here at the main circuit breakers as used golf carts follow the link below. Most trucks use the ignition key to activate a HD solenoid and a loud thunk can be heard when the solenoid engages. They are commonly called 4 wire i.e., 2 wires for power and 2 wire to activate. IMHO connect the switch at the 48V terminal Golf Cart Solenoid | eBay www.ebay.com/bhp/golf-cart-solenoid 48 Volt Golf Cart Pre-Charge Solenoid Resistor | For 48 Volt 400 Amp Solenoids. 8.50. Buy It Now. DC Battery Disconnect Switches. WhisperPower www.whisperpower.com/au/4/24/products/battery-switches.html

I have 4x 12v AGM battery connected in series for a total of 48V. I would like to be able to switch off the circuit using a 12V 30A switch. How much voltage would be accross that switch in the off/on position if I was to install it between the first battery and second battery. ? Is it possible at all? Switch. Load.

can i connect two batteries having different voltages in parallel and connected with opposite terminals

Lucas buzek wrote: I am trying to figure a solution for my problem. Connecting 8 12V batteries for 24V charge and dual 24V and 96V outputs. Would diodes on the terminals of each battery cell be sufficient to prevent short circuit? Current configuration is 4 batteries connected in parallel for higher capacity and then connected in series for 24V charge and output. And I’m thinking of adding another layer of wiring to connect all 8 batteries in series (with one-way diodes to prevent short circuits) to achieve 96V output. Is something like this possible or should I just use a voltage booster? Lucas The first problem to overcome is how to charge 96V, that is 12×8 in series. Series connections prevail over parallel anytime. Second you do not say what you are running at each voltage The easiest way is to to series to 96V and tap off at 12V and 24V and keep the power swirling around with 4 x 30V solar panels and a 96Vdc controller. I know the purist wont agree but this is economics. I had a 48V 800Ah system a few years back and tapped in at 12V to run my stereo, ran it 2.1 config, 2 bridged 700W pioneer car amps for left and right and a third 700W for dedicated base. Could hear it kilometers away (the advantages of living in the bush where the closest neighbor is 50K south) All the purist said it would not work but did for a few years anyway. Started out using it as a homing beacon whilst metal detecting for gold. The speakers took up most of the room on the truck. The second option is to get DC /DC converters to do the job and again depending on the draw and budget Keep me posted on how the diode thing progresses Remember. need is the mother of creation Cheers robbo

On June 17, 2017 at 10:12am WILLIAM MARINI wrote: if I have 2 12 volt batteries and wire them in parallel to jump start a another car will I have more kick? Wiilliam If you have a lot of cars and want to make a permanent setup for both cars and trucks do what they do in Smiths, car/truck auctions in Perth WA, where cars trucks earth movers all end up with dead batteries. One of the employees says it must be a battery grave yard where they come to die. The big Cats and Komatsus take a lot to kick over so they built a hand cart with solar panel as a jump starter kit with 24V @ 250Ah. The leads are 90squared cable, about the thickest welding cable around and a solenoid to make and break once the leads are on. As the yard boss explained its not so much the AH but with the solar charging the batteries are always topped up to 28.8V. When starting cars and 4WDs ather than reconnect to 12V they simply get you to turn the key then they hit the solenoid and bingo. All the power goes direct to the starter and doesnt do any damage I have an old SR5 Toyota as a beach bomb with a dead alternator thats 1200 to replace, so I charge it of the solar. I notice that when fully charged it starts in a second, instantly. But as the battery get lower it still cranks over but takes longer and longer to start. A HUGE difference in cranking speed between 13.2V and12V. Word of CautionNever connect Aligator clamps to a bare lead terminal as if by accident the polarity is wrong you will blow off the terminal or worse have the battery explode in your face with a shower of acid over everything. always use battery clamps to protect the terminals.and use silicone paste when installing battery terminals to stop dry joints Yep 2 x12v batteries will give more grunt but only if both are over 12.6V Cheers robbo

On February 2, 2017 at 3:20pm drich5 wrote: I am trying to connect 8 12v 155ah agm batteries in parallel to achieve a perfectly balanced charge and draw. Where might I find a wiring diagram? Ahhhhh to paint a picture in words Question 1. why would you need to parallel 8 x 12V batteries Answer better to keep higher efficiency and go 96Vdc series. this will give the batteries a better life and if you intend to hook them to an El cheapo 12V inverter with a stepup transformer of 20 to 1 you will need all of 1,240AH to last a night. Wiring. you dont state the draw/discharge you require. but a 155AH AGM have a peak discharge of 2250Amps and realistically 155Amps for 1 hr. as a guide 150Amp welding machines use 35mm squared cable for a 2 meter earth cable. Put simply buy the connector or bridging cables rather than DIY., its cheaper. Schematics of hook up. row up all 8 batteries in a single line, that about 2.2M, Preform all cables so they are NOT under tension when installed. Connect all the positives together from left to right, ditto for negative.Use quality silicone heat and electrically conductive silicone paste between terminals and connectors/bridging cables.Use torque wrench for correct settings and DO NOT over tighten Now you should a a single Now you have a single1240Ah 12V battery. A word of CAUTION the SHORT CIRCUIT amperage is 90,000amp. (12x7500Amp) an explosive force you dont want to experience. Use insulated tools, its only one spanner so buy if you dont have. Worst case shrink wrap socket extension bar and torque wrench, use electrician glove and approved safety glasses Tapping. when tapping into a parallel setup have the positive at one end and negative at the other end. It does not look as pedantic but this is the only way to get the power to flow. If both terminals are on the same battery a huge drop in performance is noticed. Maintenance torque terminals once a month to manufacturers specs. Check and log each Batteries SOC (state of charge) and if lower than average remove from string and give a de-sulphate charge Myself I am a series man Volts over Ah any time. Hope this answers something Cheers robbo

Sierra Marson wrote: I’m trying to run a dc12-2amp stereo off a battery pack with 4 5”-5” speakers and was wondering how big does the battery pack need to be to run say 5…6 hours on a single charge if you use AA 2A 3000mAh 1.2 V Ni-MH rechargeable batteries? Sierra DO the math. 12vdc@ 2 amp draw for 5 or 6 hours equal 10~12 Ah. The average car fridge draws 2.5amp and are traditionally wired to a second 100AH battery. Cheapest solution is go to the wreckers and get a half decent small car battery for 20 or a six pack for one of the guys, and a six pack for my tip Cheers robbo

Louis wrote: I have a 240 watt Solar panel (7.85Amp), 2×102 Amp Deep Cycle Batteries and Two 1500 Watt Inverters. I need to run 2 (perhaps even three) computers for 9 hours per day from them. What is the best way to wire and do my setup so that I will not run out of power within the 9 hours of each day. We have 5.5 hours of Solar ideal sunlight per day. Is this possible or should I get another battery and connect my 80 Watt Panel up as well? The solution is in the last line. hook up the 80W panel to a 10Amp controller and the second inverter. Simply split the system. Given that your 240W panel gives 7.8AMp that makes it a 30V panel, which is ideally matched to your (Calculated 240/7.8 =30 V) so just check that your 80W panel is the same voltage. For a good deal on batteries with free shipping go to http://yangtze-solar.en.made-in-china.com/product/RCKEQsZOZmkG/China-3-Years-Warranty-Free-Shipping-12V-Lead-Acid-Storage-Solar-Battery-200ah.html. Have just ordered 8 pieces and including handling costs they are under US200 ea Clarification AGM = Absorbent Glass Mat, which use Sulfuric Acid Thixotropic Gel as electrolyte. These batteries are still sometimes referred to as lead acid, but dont produce as much gas and have safer handling Remember. the poor man buys twice Cheers robbo

I have 10 batteries and I want to connect them to a home solar system, each battery is 12V 100A. How do I connect all 10 batteries that I’m just getting a 24V 500A? Easy. just parallel 2 strings of 5 x 100Ah in each string. What you want is two separate batteries connect in parallel then couple the !2vdc positive on string (A) to the negative(-) of the second string (B). String A will have the (-) negative pole and string (B) will have the pole Just look at how they series 2 x 12V to give 24V in a truck Output=Discharge. Batteries when measured in Ah is a rating of how many amps are produced, Example, a 100Ah battery gives 10 amps for 10hours a 0.1C. or 100amps a 1C for 1 hr A 100Ah battery has a C or capacity rating of 1C=100Ah. using 5 x 100Ah in parallel then series to 24Vdc gives 50amp discharge @ 24Vdc for 10 hrs @0.1C. Charging 0.1C to 0.3C ~ 50 to 85 amps @ 24Vdc Solar panels. should be 1,5 to 1 above the voltage of the bank and in your case 36V is ideal. string 10 x 300W in parallel. Note : the solar charge controller should be double the desired capacity as heat build up on hot days actually deducts from the said output once everything gets cooking. If you still have to purchase a charger again make sure its a MPPT as they are 30% more efficient than the older PWM (pulse width modulation) If you have NOT got a 24Vdc inverter yet go for the most efficient use of 10 x 12Vdc batteries which is a 120Vdc input inverter. Check that its maximum power point to point transmission (MPPT) with inbuilt charger 150Amp in your case.Check that it is at least IP65 (or better) encapsulation for weather dust ants insects etc. The fan cooled models blow all sorts of debris around as dust and a lot of that dust is conductive and/or corrosive. For longer life of your inverter open it up and use a Quality PCB surface spray as this reduces corrosion and eventual shorts. These guys make a good quality and yet affordable inverter. the link is for their 384VDC 3 phase units. This partly answers myprevious post when I asked what is the maximum voltage batteries can give in series. Some units even double this input http://golden-electric.en.made-in-china.com/product/FCzQsKnPhrcx/China-High-Efficiency-5-Years-Warranty-Solar-Grid-Tie-Inverter-3-Phase.html Hope this answers the question and not raise more. Cheers robbo

Hello, I also came up with a question:) Is it OK to connect several series of cells in paralel? (for example, I connect two 3s2p packs in paralel)

I have 10 batteries and I want to connect them to a home solar system, each battery is 12V 100A. How do I connect all 10 batteries that I’m just getting a 24V 500A?

I’m trying to run a dc12-2amp stereo off a battery pack with 4 5″-5″ speakers and was wondering how big does the battery pack need to be to run say 5. 6 hours on a single charge if you use AA 2A 3000mAh 1.2 V Ni-MH rechargeable batteries?

Steve if you are raising both voltage and mah you will need to run both in series and parallel. Parallel raises mAh and series voltage. It’s done all the time for example with two 12v 5000 mah run parrelal to make 12v 10000mah and then run in series to bring from 12v to 24v 10000mah. This would require 4 batteries to achieve these results.

I have a golf trolley battery with 2 x battery packs of I believe if my calc’s are right of 16 x 18650 batteries @ 1600 mah with one pack each side linked this makes 14.4 v @ 12800 mah. my question is how would these be wired ?? both individually and then together?

Hi People. Does anyone know what is the most 12vdc AGM abateries that can be connected in series? I sould ideally like to connect 20 or more to get 240VDC. Is this possible. Traditionally we get 24, 48 0r 96VDC banks connect to an invertor. which uses a transformer with setup up of 10, 5 or 2.5 to one to give us the desired 240 out A 240VDC rail would eliminate the wasteage of windings Thanks in advance Robbo

I have a 240 watt Solar panel (7.85Amp), 2×102 Amp Deep Cycle Batteries and Two 1500 Watt Inverters. I need to run 2 (perhaps even three) computers for 9 hours per day from them. What is the best way to wire and do my setup so that I will not run out of power within the 9 hours of each day. We have 5.5 hours of Solar ideal sunlight per day. Is this possible or should I get another battery and connect my 80 Watt Panel up as well? We are in South Africa.

Had my RV trailer worked on 6 months ago. The shop replaced my 2. 12 volt batteries with 2. 6 volt batteries. Just took the RV out for a long weekend and the batteries kept blowing the 30 amp a/c fuse or the trailer. After testing, the new batteries are the problem. When tested, both have reversed polarity?

if I have 2 12 volt batteries and wire them in parallel to jump start a another car will I have more kick?

Hello, Can you please send me the picture of cell arrangement of Marathon Nickel Cadmium battery with 36H120 cells in it for model TMA-5-20C. Thank you

I am trying to figure a solution for my problem. Connecting 8 12V batteries for 24V charge and dual 24V and 96V outputs. Would diodes on the terminals of each battery cell be sufficient to prevent short circuit? Current configuration is 4 batteries connected in parallel for higher capacity and then connected in series for 24V charge and output. And I’m thinking of adding another layer of wiring to connect all 8 batteries in series (with one-way diodes to prevent short circuits) to achieve 96V output. Is something like this possible or should I just use a voltage booster?

Great site and discussion. I just started a company with an energy storage and generation product and have secured my first customer. Functionality, reliability and cost are some of its hallmarks. I’m seeking a way to charge three or four 12V 200Ah AGM batteries that are connected in parallel which is connected to an inverter. Short of switching individual batteries in and out of a system to accomplish this, is there a way to use a marine or automotive battery charger to directly charge the system? Thank you for your help in advance Corey Fleischer Founder GMI corey@greenmachinesinc.com (310) 387-2400

how do i create 52V 26AH battery and use what type of battery model for E-Scooter? some says that LG battery is the best among all battery it that true? Thank you.

I have 48v 30a 16s cell Bms Circuit so Kindly suggest me which capacity battery i use for this also suggest me its diagram.

Your pictures and explanation for parallel connections are misleading. Capacity (mAH) is increased fourfold and NOT “current handling”. Do not confuse capacity (mAH) with current drawn (mA). Need to update your pics / article to make it clear. Other than that your post is very helpful. Here a good video about the difference: https://www.YouTube.com/watch?v=cxkVxi9P0EA

I am trying to connect 8 12v 155ah agm batteries in parallel to achieve a perfectly balanced charge and draw. Where might I find a wiring diagram?

@ John D.: OK ! Of course, you need a 1500W or 2000W (better) true sine wave inverter at 24V input voltage. I recommend a 24V inverter because the currents at 12V will exceed 1500W/12V/0.9 ~ 140 A and the conductors will be very thick, heavy and hard to work with them : AWG4 (~ 20 mm.sq.). In 3 minutes, the energy consumed will be 1500W/0.9 x 3/60 = 83.3 Wh. So, you need a Li-Po battery (more resistant and tolerant than Li-Ion) having 24V/3.7V ~ 7 cells in series and 25C (discharge rate) x capacity 70 A. The capacity is 84Wh/24V = 3500 mAh, if you discharge 100% the battery (ideal). For safety temperature and acceptable lifetime of battery, it’s better to discharge 50% the pack. So, I think a 7S2P battery containing 2 x 7 cells, 3.6V 15C.25C =3500mAh each will do this task quite well. After studying the offers and prices, I realize that it’s difficult to find and connect 7 cells in mixed mode, so the battery pack can be 8S2P, composed by 2 groups in parallel of 2 x 14.8 V 3000. 3500 mAh 15c. 25C (in series). The battery cost will be somewhere at 120 US. The battery pack weights ~ 1.5 Kg, life cycles will be ~ 60 and the charger is expensive. Almost any 24V inverter accept 29,6V input voltage with no issues, at full load the voltage will decrease to 22. 23V. Concerning batteries, if you use two high rate 12V AGM batteries in series, like CSB HR1290W, you’ll have over 4 min. at 1500W (50% discharge rate). The batteries weight ~13.6Kg !, the cost is ~90 US, life cycles will be over 100 and the charger is cheap : you can put the batteries in parallel to a 12V charger. So. good luck !

if i connect panasonic 18650 batteries in the configuration of 3s4p then what will be my total voltage and ah

I have a New Years eve ball that i am trying to power. it has 12 led strips on it that run at 12 V and requires 240 watts per strip. i am trying to build a battery pack using the 6V Square lantern batteries. They are 6V 26000mah batteries. i currently have it setup a with 4 pairs of batteries running in series so i am getting 12V at 26000mah powering 4 strips. but the LEDs arent as bright as they should be. What would be the best way to wire these. everything i know about electricity and current i have read online. i was thinking about trying to do a series and parallel setup to power the entire thing. i need a total of 2880 watts at 12V. to power the entire thing but im being cautious because i dont want to have them blow up on me.

While this is the general rule there would be certain exceptions. When running in series one can for example use a 2 cell and a 3 cell to easentially have a 5 cell lithium battery. I.e. A 2s 50c 5000mAh battery in series with a 3s 50c 5000mAh battery will be the same as if purchasing one single 5s 50c 5000mAh lithium battery. Im not suggesting mixing brands or an old cell with a new cell however starting with two new cells of like batteries you are essentially working with the same construct of internal material. Checking Internal Resistance and using said batteries together for the life of the batteries you will be fine in this particular situation. We do this all the time in the Hobby world and see like IR ghroughout the life span and voktage drain is consistent across all the cells. If one were to use different manufactures or qualities of batteries you may find one will discharge faster than the other. Keep it simple and match the cells and brand and you wont likely have any issues.

bu-302, series, parallel, battery

I want to replicate an ac circuit that is 1500 W, and I believe under 15 A. I want to make a portable unit so that when I don’t have power, I can still do a limited amount of work. The array of batteries would have to deliver this current for about 2-3 minutes. First, is this possible with current lithium ion batteries, and if so, what would the general configuration setup look like?

I’ve replaced a failing set of cells in a battery pack for a pair of equine clippers rated at 12v with 10 Ni-Mh AAs in a parallel configuration. This seems to work ok. My question is. is it safe to charge the batteries in the same parallel configuration using the charger that came with the original battery pack. or do i need to remove the batteries and charge them in a standard charger in series. I guess i could try it and monitor the temperature of the cells.

please help me. What happens to the voltage when batteries are connected in series, in parallel and in anti series respectively?

@NabuN, thanks for the clarification. Though its a bit too technical, I managed to comprehend it. Will continue to monitor my system. Regards!

@NabuN thank you so much for taking your time to explain. Though its too technical, I could still make some sense out of it. I will monitor the system. Regards!

Hi, i want to change the old batteries on my vacuum cleaner and there is only room for 3 18650. I want to ask if i can conect 2 of them in parallel and the third in series with the other 2?

Hi. I am working on a project to make a custom solar charger with 80/100waatts panel to support 3 led lamps of 5w and 3 chargers for smartphoe or tablet devices. Could someone who has knowledge guide me what type of batteries i will need and how i can combine them to support this structure ? Thanks in advance !

@ Veng: Without wishing to argue with anyone here, in my experience over 40 years with lead batteries of 12V and 6V and degree in electrical engineering, I can say that the parallel connection of two batteries the same type and not necessarily the same capacity or age, is certainly better for their (remaining) lifetime compared to serial configuration for several reasons: 1. Capacity is larger of the assembly (equal to their sum of real capacity. ) and currents of charging/discharging smaller than if would be used only one of them. 2. SOC of the batteries are quasi-identical, due to terminal voltage which is the same for both batteries. 3. It is easier to monitor and correct the voltage of one battery than the voltage of 2 (3. n) batteries, and if a battery have cell(s) shorted, it will be seen as the terminal voltage drops and can intervene timely. Usually, most defects are with internal interruption/increase of internal resistance (in the ratio of 10. 20/ 1 face of internal shorting). In your case, for 2 solar panels with 36 solar cells maximum charge current will be ~2x150W/18V = 16.5 A, supportable by any individual battery, the better of the two in parallel. The currents will be divided thru batteries in reverse proportion to their internal resistance, in the first approximation ~9A for the 200Ah and ~7A for the other. In 8.9 hours of one sunny day they will be charged with an energy of ~ 1.6kWh (35.40% of maximum). If the inverter is for 12V, the load current will not exceed 900VAx0.6/11V=45A and is divided into ~26A through 200Ah battery and ~19A through 150Ah battery. The autonomy at maximum power will exceed 6 hours, if the batteries were loaded to full capacity. Take care to have thick and good connectors / screws to terminals and same length of cable from “output” of the 350Ah battery to each component battery. So, it can be done without much expenses, with care and attention! @ Pete: I stored SLI batteries/auto one on top of another, but only for short-term (1. 3 weeks),I even put three pieces on a vertically stack. For stationary applications I put only two batteries one of top of another, for reasons of mechanical resistance (to not crack the plastic case, in time), with spacers from rubber/plastic acid resistant, bands of 1-2 cm thick and took care to NOT cover the vent plugs. SLA and AGM batteries need a small amount of ventilation, so I simply put an expanded polystyrene between batteries. After 5 years I have no problem with them, they are NOT in a box. In a closed box it’s better to insulate all the interior walls to achieve a good thermal isolation of batteries from external medium and reduce mechanical shocks. So, can you try 3 batteries (not heavier than 20 Kg each) one on top of another with some precautions. at your own risk. and let us know about ? 🙂 Peace to all

@ Veng. mmmmmmmm Yes you can but they wont last long options A) get another battery that exactly matches the old even to the state of Decay, or get 2 new is best B) get another solar array and split your unit in two @ Pete. Never seen anyone STACK batteries, weight is one issue and air space of 50mm around for ventilation and cooling may be a problem. Battery boxes are normally made with this space allowed for as on hot days the batteries are even hotter, which increases the resistant which increases the heat the list goes on. In RVs the box needs to be constructed strongly to stop batteries flying around and arcing out( High Amps BIG sparks) and have 3/8 rubber pad for reduced vibration heat ransfer, and have a screw down frame on each battery, so as NOT to pull out terminals. Batteries are heavy and create high forces especially if the vehicle rolls or crashes. You dont want 100Kg batteries flying, then the Acid. Batteries need to be inspected regularly, even maintenance free must be checked monthly (Excide Aircraft Gel types stipulate logging each cell and checking torque of terminals each month for warranty, how many of us do it. BTW Solar is more EFFICIENT on a cooler day often with scattered Cloud, although the unit wont create as much power it does not have to as fridges in particular are not working so hard. I had experience of a large system that ran out of puff on days over 44C due to near melt down Have a look at a Cat D9 battery box takes up the whole space under operators seat. They are a work of art, but really needed for safety and hold batteries secure against all odds Robbo

hello, I want to stack 4 car batteries on top of eachother in order to put them in a case. Is that even possible? Cheers

Hi, can two 12vdc batteries of different Ah, (150AH / 200AH), be connected in parallel for increased Ah capacity (350). To be charged by 2x150W Solar PV panel via 30A solar charger regulator for lights and entertainment, in an off-grid set up? I use a 900VA Inverter.

Anthony Your question does not really give much info. 4 x 1.5V can be 6.0v in series or 1.5V in parallel. You will need to check how they are configured If the light unit is equipped with an external jack it should have on it the voltage and which part of the jack is negative. If you need to replace batteries, you can simply buy a set, and replace them when dead. If this frequency is too often then go hard wire as it seems an over kill to run a charger cable to the light for charging batteries instead of hard wiring the light, direct Robbo

Anthony : 8V seems to be OK; you must verify the voltage on all 4 batteries in series (the pack) to not raise over 1.6 V / cell (6.4 V- the pack) AND the charging current must be lower then ~ 4000mAh/4 hours charging = 1 Amp with ~(8V-6V)/1A= 2 Ohms power resistor. Of course, 4000 mAh is the cell capacity.

hello, need some help. I have an outdoor motion light in my drive way. it’s using 4 C battery’s, and would like to get a wall adapter. What voltage adapter should I get? I can get one that change from 3, 5, 6, 8, 10, or 12. Thank you in advanceAnthony Mendonca

i have to to use a maximum of 48v, cell may be one or more then one, for the maximum power what should i do &how; should use them

(a) A unit Li-ion cell/battery has average discharge voltage (3.8 V), resistance (75 ) and capacity 5 Ah. Integrate as many Li-ion cell/battery required for developing a Li-ion battery module which can produce 120 V and 150 Ah.

I have the state space equation of the 2V lead acid battery and I want to connecting 6cells in series. How can I determine the new state space equation?

@ Frederick Sure you can. But. why you connect them in series. You need to take precautions when use over 48V DC voltage. Like I wrote upper, I use 30 V DC at our off grid country house and 2…3 times by week I need 180 V DC. I had some issues, especially when the standard switch used for 230 VAC has burned out at the disconnection of a 2 KW leaf blower. Then, I mounted some suppression circuitry. In your case, for charge and equalize all batteries in the same time, you need to put them in parallel, like I do since 2011. It requires 7 times less attention concerning monitoring charge voltage. @ Brenda Your Li-Ion battery seems to be OK if the voltage is higher than 2,8. 3 V. So, first, I suspect the external AC adapter / connector of the tablet. The ability of internal charger did not depend on battery voltage, it’s monitoring the voltage and current thru battery. Second, maybe your battery is defective, I understand it’s removable. Try to change one by one with somebody who have same model tablet. @ Fahad Battery B seems to be defective. If you let batteries few hours free, the voltage will drop a little and you can measure SOC voltage. But this does not help the end-of-life battery B. From my experience, I prolonged the life of weak AGM batteries by watering them. But I did not gain much time, sometimes a week, maybe one month. The corroded cell(s) / bridge will heat, reduce the external power supplied and make smell and boiling bubbles sounds when you connect 20.30A load to this battery. I even tried to make 10V battery removing / shorting the defective cell and I learned it not worth to do this. Usually, flooded and gel batteries have a longer life. You need to buy a new pair of batteries for the solar system, same model, mark, date of production. The low cost solution, at your own risk: measure the real capacity at discharging of battery A and buy just one AGM battery of this capacity. and monitor both frequently and attentively at charge / discharge. If the capacity of A battery is lower than 85.90% of marked capacity (Ah) this solution don.t worth to be implemented, because battery A will soon be defective, like her “sister”, B. @ Nikola A group of 2 raw in parallel, each raw with 6 batteries (rating 80A…so much ?) in series, will have maximum 280=160Ah capacity and will supply maximum 160A according to specifications and the LOAD. If you want a 480 Ah battery with 480A (!!) maximum rating current from these 66 batteries of 12V, you configure them in 2 groups in series, each group containing 6 batteries in parallel. So you’ll have only 212V= 24V.

I have a Asus tablet that quit charging, my husband checked the battery, the volts are supposed to be 3.7 but it tested 3.2. Could this influence the tablets ability to charge? I would rather replace a 40 battery than pay a 200 service fee. Thanks, Brenda

I have installed off grid solar system at home. Its 24v system. After two years all of a sudden battery backup time reduced to 40 min. I checked the voltage of both batteries. battery B voltage drops quite quickly during on load condition. While on full charge condition both batteries have the same voltage. One if my friend was saying that after changing these batteries switched off the whole system for 3 t 4 hrs and let batteries to settle or balance. Please help me in this situation. what should I do with AGM batteries

Hello. I understand the series addtion of volts and the parallel addition of amp hours but my question is what happens to the resultant continuous current or max current that a battery can handle in the following configuration example: If a single 12v lithium 80ah battery has a continuous current rating of 80 amps what would happen to the continuous current and max current ratings of the new resultant battery where 6 of these are connected in series to have 72volts and another 6 are added in parallel to have a total of 480 ah? Do the continuous and max current ratings also go up and would it be 480 amps? Thank you in advance.

George. 1, 2 3. Vide supra. The answers are on this page. On the other hand, you may be doing something irregular with your batteries. the batteries don’t like it. you are looking for explanations.

I have some questions to ask and will be very happy if the knowledge gurus will assist me, thanks 1. Why do parallel cells get exhausted easily when not in use? 2. Why does the same amount of current flow through each individual resistor in series but a different amount flows through all in parallel? 3. Why does the voltage differ across resistors in series but the same across all in parallel?

George. Batteries connected in parallel do not loose charge when not in use. There is nowhere for the power to go. I personally would never connect batteries in parallel. Batteries are never identical. They get out of step. If they are connected in series, they can be equalized. If they are connected in parallel, they cannot be equalized.

Hi, I will be very grateful if I can be educated on whether batteries in a parallel connection will continue to loose charge even when not in use. Thanks in advance

hi there just wondering if its a good idea to connect a motorcycle battery and a car battery in parallel to increase the life time of the battery pack I build, thanks in advance

Great info thnx guys. I have a solar system with 24v charging using 2 x 12v 100ah batteries in series. One connected to an inverter, the other to lights. They have different discharge rates and are at different voltage levels at times. Is it good set up or do we have a problem.

Shola, NanuN. If batteries are connected in parallel, they will get get out of step and will progressively get more out of step. Some of them will fail prematurely, regardless how the entire group is charged and/or discharged. The only viable solution is to disconnect, give each series string an individual equalizing charge, and do this on a regular basis. Connecting batteries in parallel is a very bad idea. Solar vendors will cheerfully sell these configurations because the competition is fierce and they automatically look for the cheapest batteries to sell. There is a bigger turnover in smaller batteries, hence these batteries are less expensive in parallel than unparalleled bigger batteries. I have a solar backup and use a high ampere-hour non-paralleled string, which I purchased regardless of what the salesman was trying to sell. A proper solar controller will automatically seek the maximum power point, and then charge the batteries in bulk mode (at maximum power), then absorption mode (voltage limited), and finally float (reduced voltage). It is a good idea to limit bulk charging to C/5. NabuN. Batteries/ battery cells on equalizing charge never develop the same voltage during or immediately upon completion.

Amin wrote: In figure 3 and fig 4. can charge it? Even one of those are not equal to each other batteries. Yes, you can ! With some extra work, of course.  Like humans, batteries are not identical each other. I consider in this case only batteries of same capacity, voltage and mark, in state of order. This means their real capacity is over 80 % of marked capacity and they have different state of charge. In series, the charge current will bring at full first the weakest battery, theoretically. For safer charge, you must monitoring the battery/cell with the highest voltage, (the voltage to not overcome the upper limit recommended). “The weakest element of the system will give the strength of the system”. So, you must remove the weakest element to not have complications and problems in next future, and to ensure a good performance of the string. In parallel it’s easier, the strongest battery will help the weakest. They would last longer. Before connecting in parallel, it’s fine to verify each battery for self discharge or even internal shorted battery, to not deplete the good ones (defective batteries/cells). In my solar system, from 2011, I use over 50 batteries mixed connected, usually in parallel when I need 30V and 10A. 30A for lighting and 1,2 kVA inverter UPS. and in series, 180V DC, (for circular saw and tools at 230V with universal motors, enough to work satisfactory). Since 2013, each year, 1. 2 batteries, the oldest, had to be removed, which is quite normal, I think. Shola wrote: I have a series/parallel battery pack made up of 6 12V 200AH/10HR batteries (2S3P setup). My questions are as follows what will be the ideal charging current for the setup, secondly will the charging current be the same at each ve terminal and finally is it true that one set of batteries will get fully charged/discharged before the other or they get fully charged/discharged at the same time. Thank you in advance for your enlightenment. Ideal charging configuration it’s the 2 groups in parallel (12V), because all batteries will have the same voltage. But it’s not easy to change the connections with thick wires and screws two times at every cycle, I believe… So, you have 2 groups connected in series of 3 batteries in parallel, each. In accordance with the manufacturer’s specifications, recommended charging current will be, I suppose, 10% of the battery capacity. For 2S3P setup, the bulk charge current will maximum ~60A, and voltage will not overcome 28V, usually. A smaller current will be fine, 40.50A. As I said at the beginning of my post, the two branches currents will be close, should not differ by more than 10%, let’s say 24A and 26A it sound OK for 50A charging. When charging, especially during equalization, batteries will reach almost the same voltage each. The lead and NiCd batteries have this feature. When discharging, the weakest group of 3 batteries will have the lowest voltage, so you need to stop discharging at a voltage higher than the limit, let’s say 11,8V under maximum 60A load. It’s good to not discharge more then 30.50 % of battery capacity to achieve a long life. Read the manufacturer’s recommendations, I learned a lot from these datasheets.  Have a good work !

Shola. Batteries that are connected in series automatically always carry the same current, (at each positive terminal), regardless of whether they are being charged or discharged. They will have slightly different ampere-hour ratings due to tiny differences in materials, in processing, and so on, incurred in manufacturing. They will also possess slightly different self-discharge rates for the same reason. They will get out of step very slowly, over time. Hence some will become discharged while other still carry some charge. It is something that is easily overcome by giving the entire string a low current overcharge from time to time. This is called an equalizing charge. The first to become fully charged will gas until the last becomes fully charged. After that all the batteries will be in step again, at least for some time. Sealed batteries either cannot easily be be equalized or cannot be equalized at all, hence their cells become hopelessly unbalanced, hence they have relative short lives.

I have a series/parallel battery pack made up of 6 12V 200AH/10HR batteries (2S3P setup). My questions are as follows what will be the ideal charging current for the setup, secondly will the charging current be the same at each ve terminal and finally is it true that one set of batteries will get fully charged/discharged before the other or they get fully charged/discharged at the same time. Thank you in advance for your enlightenment.

Hello to all, For Ray : 1. I had one e-bike with AGM 3x12V 10Ah defective battery, 36V system. After long tests, I upgraded the battery box in dimensions, voltage and capacity with AGM 4x12Vx (2x7Ah) 1x6V (2x7Ah) = 54 V 14Ah, batteries for UPS, high rate. My chinese controller supports 60V with no problems, after I changed all electrolytic capacitors to 100V (and Power FET to 80A/100V). Now, I have 4 years of use for my e-bike and the 350 W hub motor (only.) can push me to 35 Km/h. The range is ~ 30Km, because I like speed 🙂 [ I am from Romania and the bike was made in Hungary, I presume ]. So, in your case, I do the math : 48V / 3,7V = 13 cells in series 20Ah/2Ah = 10 cells in parallel You ~right, you need 130 good cells 18650 Li-Ion, it is a 13S10P battery. It goes OK with 12S10P=120 cells, or 13S9P=117 cells, but range is reduced. 12S10P it gives more range compared to 13S9P, but lower maximal speed, in my opinion. Maximum voltage after charging is 4,2V x 13 = 54,6 V (for 13S10P). The range and life for battery is affected by the Voltage disconnect of the controller, of course. The controller accept 60V with no problems, so looks OK to me. 2. Until 2012, I tested my batteries by discharging ~ 50% with a 12V 21. 55W halogen bulb from car, a clock and an ammeter. Then, I get one “Watt’s up meter” for RC hobbysts which ease the measurements with my old bulbs ! 🙂

If We have two groups of batteries in parallel ,each group consist of 9 batteries in series. the system is 110 Vdc. because of one defected battery in the second group the non-ability to disconnect this group from the battery dis-connector.we will disconnect the battery only from the group keep its circuit open.also open the loop in many another points. But finally we will keep the positivist connected to the first battery the negative connected to the last battery all in between open. is this right,what is the side effect to the second working group.

I am trying to build a battery pack for an e-bike conversion, the motor uses 1000W and is a 48V system. I want to use some salvaged lithium batteries I have been collecting from work. Target battery pack size is 20Ah / 48V DC. The battery packs which I am getting from work are designated as 14.8v dc, 6.15 amps, and 91.02Wh. I have already opened up a pack and know there are 12 18650 lithium cells inside. unfortunately no info is written on the cells. I measured them and all are at 3.65v dc. If I do the math with the above pack parameters then each cell would have a capacity of 2000mA and a nominal charge of 3.7v. To get to 20Ah for the battery I would need 9 serial strings in parallel, I think the annotation is 13S9P, 13 serial and 9 parallel strings. 121 batteries total. does that sound correct? Is there a test I could do to really determine the Ah capacity of a cell rather than rely on the documentation on the pack?

I have done 3KW solar power generator for home. Battery getting charged by pm everyday. I have used 48 v system with 12V 200Ah 4 batteries in series combination. In night, I want to charge my REVA Electric Car and battery is going to Low cutoff value (10.8V/battery) and power is switching off in night. I plan to increase capacity from 48V 200Ah to 48V 300 Ah in Series and Parallel combination and improve the power discharge REVA car consumes 3-4 KWh units of electricity every day. Please suggest any alternative for my requirement. How much battery to be discharged every day for long life of battery? Can I use 7.5 Kilo watt Tesla battery? Please suggest remedy.

If one lithium battery at 12 volt has 100 amp recommended charge rate, does 2 of the same in parallel charged together have 200 amp charge rate?

Custom 72V Lithium Battery Solution for Industrial Equipment

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Why to Select TLH as Your Custom 72V Lithium Battery Provider ?

TLH is one of the leading 72V Lithium-Ion Battery manufacturers. We have proved ourselves by manufacturing quality products for the last 15 years. It takes the hard work of our engineering teams to satisfy 500 customers from all over the world.

Our R D has developed 72V battery pack for marine boat,van ,motorcycles and UPS ect.We can design 72V battery as triangle ,rectangle and square shape.

We can provide the capacity from 10Ah.50Ah of our 72V lithium battery for electric bike.

If you want to have a customized 72V Lithium-Ion Battery for your projects, do let us know we will get back to you as soon as possible.

Strict Quality Control Process for your 72V Lithium-Ion Batteries

  • Strict quality control system to ensure international standards of ISO 9001:2015 by TUV.
  • Each 72V Lithium-Ion battery is tested comprehensively like charge and discharge tests.
  • All cells are randomly checked before use and select in strict standard in battery pack.
  • The record of each 72V Lithium-Ion battery test is maintained and can be shared with the client upon request.

TLH: Your Best Partner in the Manufacturing of 72V Lithium-Ion Battery

The TLH company has been manufacturing outstanding quality lithium battery packs for 15 years when Shenzhen Tianlihe Technology Co. Ltd. started its modest head start and has more than 500 customers from all over the world. We produce quality products with the help of an experienced R D and quality control team. We try to give out maximum output in minimum leading time for the satisfaction of our customers.

72V Lithium-Ion Battery is used in Electric Bikes and Scooters. If you are a manufacturer of E-Bike or scooters, you can call for us to make a customized battery pack for you with customized dimensions. These battery packs can also be used for solar applications and electrical appliances that require high energy density supplies.

We have our sales offices in UK, USA, and Germany. Our sales team is very professional, having experience of dealing with customers from all over the world. We try our best to give maximum efficiency with minimum lead-time.

If you have any kind of suggestion, demand, or feedback related to 72V Lithium-Ion Battery, feel free to connect with us!

v Lithium-Ion Battery – The Ultimate FAQ Guide

The following FAQ Guide consists of all the important queries about a 72v Lithium ion Battery Pack.

To get answers to your questions, Have a look!

  • 1. What does wh on a 72v lithium-ion battery means?
  • 2. What kind of charger is used for a 72v lithium battery?
  • 3. What can be the reason for my 72v lithium battery not charging?
  • 4. How can you maximize your 72v li-ion battery’s working?
  • 5. How long do 72v lithium-ion batteries last?
  • 6. How can you charge your 60V lithium battery?
  • 7. What measures should be taken while using a 72v lithium battery?
  • 8. How can you install your 72v lithium-ion battery?
  • 9. How to build a DIY 72v lithium-ion battery?
  • 10. Are 72v lithium-ion batteries safe?
  • 11. What does the built-in protection system mean in a 72v lithium-ion battery?
  • 12. How to replace a 72v lithium-ion battery?
  • 13. What are the uses of a 72v lithium-ion battery?
  • 14. Is a 72v lithium-ion battery dangerous?
  • 15. Can a 72v lithium-ion battery be explosive?
  • 16. How can you charge your 72v lithium-ion battery?
  • 17. What is the transport process of a 72v lithium-ion battery
  • 18. How do you know if your 72v lithium-ion battery is bad?
  • 19. Is 72v lithium-ion battery stronger than other batteries?
  • 20. What is the charging time of a 72v lithium-ion battery?
  • 21. How can you store your 72v lithium-ion battery?
  • 22. Under what conditions does the battery work best?
  • 23. What are the main factors due to which a 72v lithium battery should be considered?
  • 24. How do you know if your battery is not working properly?
  • 25. What can cause the 72v lithium-ion battery to die?
  • 26. Can a damaged or leaked battery pack be used?
  • 27. How long will a 72v lithium-ion battery last if not used?
  • 28. How can you check your battery voltage?
  • 29. Does a 72v lithium-ion battery die if not used?
  • 30. At how much battery percentage should you store your 72v lithium battery?
  • 31. How can you fix your 72v lithium-ion battery if it won’t charge?
  • 32. How can you dispose of your 72v lithium battery?

What does wh on a 72v lithium-ion battery means?

Wh stands for watt per hour and is a unit of energy or power that is equal to one watt in one hour of time.

This term is commonly used in electrical appliances.

The wh on a 72v lithium battery means the energy that can be stored on the battery.

The power is subjected in watt-hours and is the voltage that the battery provides which is multiplied by the amount of current a battery provides in that amount of time which is usually measured in hours only.

What kind of charger is used for a 72v lithium battery?

A 72 v lithium ion battery has a built-in protection system to absorb any shocks or extra current or voltage that may be delivered.

Lithium batteries require a charger that delivers constant current or constant voltage.

Some 72 v lithium batteries may require special 84V lithium battery chargers only for effective working and long term life.

The charger that comes with the 72v lithium ion battery is recommended to be used for effective working.

However, constant use of inappropriate chargers can ruin the battery’s working and effectiveness completely.

Figure 1. A 84V lithium ion battery charger for 72V lithium battery

What can be the reason for my 72v lithium battery not charging?

A 72v lithium ion battery refuses to hold a charge when its charge amount has dropped below the standard limit.

The lithium ion cells do not recover if their voltage goes down a particular level and the cell is generally dead.

If your 72v lithium battery does not hold a charge or drains abruptly, consider recharging it fully so you might save it.

However, this might be due to overcharging or extreme self-discharge which makes the battery malfunction and not hold a charge.

How can you maximize your 72v li-ion battery’s working?

You can maximize your 72v lithium ion battery’s life and effectiveness by taking proper precautions while using it. A battery may work for longer runs without any malfunction or not work at all depending on how it is kept and used.

  • Any kind of mishandling should not be preferred.
  • Do not overcharge your battery beyond its limits as it damages the battery completely from the inside.
  • Charge the battery fully after complete discharging every two to three weeks.
  • Keep the battery clean from dirt or corrosion.
  • Do not leave the battery to charge for long periods of time.
  • Keep your 72v lithium ion battery away from direct sunlight.
  • Keep the batteries in cool and dry places away from any metal or flammable products.
  • Charge your 72v lithium battery before storing aa itself discharges itself and will drain if it is kept unchanged.
  • Keep charging the lithium battery for short intervals.

How long do 72v lithium-ion batteries last?

Typically a 72v lithium ion battery is expected to have a life span of 2 to 4 years.

A battery should be well maintained for proper and long working periods.

Whereas a battery tends to lose its capacity slowly with time whether it is being used or not.

The lifespan of a 72v lithium ion battery may differ due to the circumstances it is kept.

The temperature plays a major role in the working and charging of a battery.

If a 72v lithium battery is well maintained and managed it may last for up to 5 or 6 years and on the other hand if the lithium battery is mishandled it may only last for a year or less than that.

The working of a 72v lithium battery greatly depends on the handling and care.

What are the advantages of a 72v lithium-ion battery?

Lithium ion batteries provide a wide variety of functions that serves as advantages.


The 72v lithium ion battery has an enhanced safety feature which makes it easy to be used indoors without any risk of accidents and eliminating the risk of explosion or dangerous battery acids.

Fast charging:

The lithium batteries provide fast charging which means it takes less time to charge and provides more working hours. Also, a 72v lithium battery encourages short charges so the battery does not have to charge for full cycles at least for a month or so.


Weight is a great aspect to be considered in the use of electrical appliances as they provide mobility. 72v lithium batteries provide great mobility as well as size customization with a longer life span, low self-discharge rate, longer working time, and fast charging as compared to other batteries.

Eco friendly:

72v lithium batteries provide numerous environmental benefits over fuel-burning batteries. As electric vehicles are increasing, a reduction in carbon emissions is seen.


Unlike other batteries whose water level needs to be monitored, lithium ion bases batteries do not use water. This factor makes the lithium batteries require very little to no maintenance as well as eliminate engine maintenance.

Figure 2. A 72v lithium ion battery pack

What measures should be taken while using a 72v lithium battery?

A 72v lithium battery is the safest of all kinds however can be dangerous at times.

Prevent the batteries from direct contact with sunlight.

Store batteries at cool, dry places away from any flammable products so they may not catch fire.

Keep the lithium batteries at room temperature and avoid high or low temperatures.

How can you install your 72v lithium-ion battery?

The installation of a 72v lithium battery can be very easy if proper steps are followed.

The user manual that comes with the battery should be read thoroughly for adequate installation of a battery.

The following link leads to a tutorial on installing a 72v lithium ion battery.

How to build a DIY 72v lithium-ion battery?

You can build a DIY 72v lithium ion battery at your home on your own just by using a few things.

The following link shows the method to build your own lithium battery pack.

Are 72v lithium-ion batteries safe?

The 72v lithium ion batteries are the safest if used properly by following the user manual.

All batteries carry a safety risk and manufacturers are obligated to assure customers with safety measures.

A lithium battery works safely with proper precautions taken and under the encouraged circumstances.

The temperature where the lithium battery is kept should be moderate.

Harsh temperatures should be avoided as they trigger the 72v lithium batteries to lead to unwanted situations.

The use of damaged or leaked batteries should be prohibited as there are greater chances of explosions.

If proper measures are taken while using a 72v lithium battery, they are the safest batteries to use.

What does the built-in protection system mean in a 72v lithium-ion battery?

The 72v lithium ion battery consists of a built-in protection system in the circuit that monitors the voltage being supplied or given out by a lithium ion battery and disconnects the battery itself if the charge level goes too high or below the standard level.

This protection system secured the battery against any malfunctions to occur which include the threat of short circuit, overcharging, monitoring, or balancing the entire working of the battery

How to replace a 72v lithium-ion battery?

You can replace the 72v lithium ion battery in your electrical appliances very simply by just following the instructions given in the user manual.

Read the user manual thoroughly before doing any sort of work with the battery for effective and correct usage to be carried out without any difficulty.

What are the uses of a 72v lithium-ion battery?

A 72v lithium ion battery is designed to carry heavy loads as well as give out competitive working.

These lithium batteries are perfect to be used for electric scooters, electric bikes, solar panels, and other high-energy demanding electrical appliances.

They are used for powering most of the remote appliances as it is now an electric world, with all kinds of electrical appliances which require batteries with the best working capacities.

Is a 72v lithium-ion battery dangerous?

A lithium ion battery is manufactured to assure most of the safety concerns of the customers.

However, The 72v lithium ion batteries can be dangerous if they are damaged, broken, leaking, or mishandled.

If a battery is damaged or leaking it should not b touched as it can cause extremely dangerous situations.

Mishandling and not using the 72v lithium battery with proper care can lead to the battery creating unwanted dangerous circumstances.

If the battery is properly handled and maintained, there is no danger.

Can a 72v lithium-ion battery be explosive?

If the 72v lithium ion battery is kept and used under unfavorable conditions, it may lead to explosions.

Following situations may cause the battery to explode:

  • Using a damaged battery pack.
  • Overheated or Overcharged lithium battery back.
  • If the battery is kept in direct contact with sunlight.
  • Constant Unfavorable temperatures.
  • If flammable objects are kept close to the battery.
  • Corroded terminals of the battery.

Figure 3. An exploded battery pack

How can you charge your 72v lithium-ion battery?

Charging a 72v lithium ion battery is as simple as charging any other electrical device.

To use the charger that comes with the battery is recommended otherwise any charger that has a set level of current can be used.

If the battery has a built-in protection system, the charger goes off on its own once the lithium ion battery is charged.

If it does not have a safety system, the charging should be monitored and plugged off as soon as the battery is charged as overcharging effects the effectiveness of the battery.

Charging the battery for smaller cycles is encouraged rather than discharging and recharge completely.

What is the transport process of a 72v lithium-ion battery

As 72v lithium-ion batteries consist of hazardous material, they are banned to be shipped by air however can be transported through water or highway.

Proper packing and stacking of the battery are encouraged to prevent any unfavorable conditions to occur.

How do you know if your 72v lithium-ion battery is bad?

The easiest and quickest way to check your 72v lithium ion battery’s status is through a voltmeter or a multimeter.

Connect it to the battery to check the voltage.

If it is below the standard level it means that the battery is not holding a charge and working improperly.

However, there may be other reasons that include the lithium battery being old, due to leakage or damage, swollen battery, or overcharged to a level that they die.

Figure 4. A voltage measuring device

Is 72v lithium-ion battery stronger than other batteries?

The lithium ion batteries are designed to be 2000 times more powerful and have the capacity of over 1000 charge cycles.

The 72v lithium battery is the strongest as it gives out dense energy due to heavier current capacity and can work with high energy demanding electrical appliances.

What is the charging time of a 72v lithium-ion battery?

A 72v lithium ion battery will take around 10-15 hours to fully charge once it arrives.

Later the battery should be charged for shorter cycles after every use.

Discharging the battery and recharging it completely should be done once every 3 to 4 weeks and that requires around 4 hours.

Once the lithium ion battery is fully charged the current drops to a set level.

How can you store your 72v lithium-ion battery?

You can store your 72v lithium battery under certain conditions:

  • The 72v lithium battery should be kept at a 30 to 50 percent charging level while storing it as it discharges slowly on its own.
  • The temperature should be normal room temperature as high or low temperatures can affect the effectiveness and life of the battery.
  • The battery should be stored in a cool, dry place.
  • A battery should not be kept fully discharge as it may never hold a charge again.
  • Using the battery after storage periods may affect the battery working and it will not work as a new battery does.
  • The battery loses its capacity over time whether used or stored.

Under what conditions does the battery work best?

A 72v lithium ion battery will carry out its best work if used properly under the conditions it requires.

Following factors should be considered for the effective working of a battery:

  • Partial discharges should be encouraged.
  • Select the proper discharge method.
  • Avoid charging the lithium battery to complete 100%.
  • Avoid deep discharges and high current charges and discharges.
  • Control the temperature around the battery, extreme high or low temperature affects the battery working and over time will cause it to die.
  • Do not place the batteries in direct sunlight or heated appliances.

What are the main factors due to which a 72v lithium battery should be considered?

There are several functions that a 72v lithium battery provides which makes it the best type of battery with splendid functioning. Some of the main appreciable features of 72v lithium ion batteries are as follows.

  • Longevity of the battery.
  • Low maintenance.
  • Effective long term working.
  • Can bear heavy loads.
  • Works in wide temperature ranges.
  • Provides constant current/voltage.
  • Lighter in weight.

How do you know if your battery is not working properly?

The status of your battery may be determined by monitoring its working overtime.

If the battery fails to function or causes disturbance while carrying out its function, you should know the battery is bad.

The battery may refuse to hold a charge or to discharge at a very fast rate.

Several circumstances which prove the irregular working of a lithium battery constitute to this factor.

A voltmeter can also be used to learn the battery status of your lithium ion battery pack.

What can cause the 72v lithium-ion battery to die?

The most leading cause of a dead 72v lithium battery is heat.

The batteries should be kept away from direct sunlight or extremely hot temperatures.

Overcharging should be prevented and the use of the lithium battery in extreme Hugh temperatures should be avoided as it may slowly lead the battery to overheat and die.

Due to such excessive conditions, the cells of the battery pack die and refuse to hold a charge which results in the failure of the lithium ion battery pack.

Can a damaged or leaked battery pack be used?

A damaged or leaked lithium ion battery pack can be extremely dangerous to be touched.

The acids of the battery can burn your skin and cause several problems if they come in direct contact with your skin.

You should not try to operate the damaged lithium battery pack as it may explode and cause severe damage.

The damaged and leaked lithium battery packs should be kept away from appliances and households and should be handed over to the recycling stations or e-disposing centers immediately.

How long will a 72v lithium-ion battery last if not used?

If a 72v lithium ion battery is stored or keep unused it will last for 2 to 3 years, the timeline provided by the manufacturers.

However, if a lithium ion battery is in use or not its charge capacity falls with time, and the battery self discharges.

If the battery is discharged to a level that it is drained, you should consider it dead.

The stored or unused battery should be monitored regularly for its charge level and charged when necessary to prevent it from draining completely.

How can you check your battery voltage?

You can easily check the voltage or battery status of your lithium ion battery using a multimeter or voltmeter.

It consists of a monitoring screen and depicts the voltage status of the battery it is connected to, on the screen.

Simply connect the terminals of the voltmeter with the battery terminals, and it will show the respective voltage of the battery.

This is the most effective and quickest method to know your battery’s accurate voltage

Does a 72v lithium-ion battery die if not used?

The battery discharges on itself and loses its charge capacity over time whether it is used or not.

The life expectancy of an unused 72v lithium battery ranges from two to three years when not in use or are stored.

The charge status of an unused battery should be monitored so it does not go bad before time.

At how much battery percentage should you store your 72v lithium battery?

The lithium ion batteries are considered to be stored while they hold 30% to 50% battery capacity because the battery has its self-discharge component which causes it to use the battery over time slowly even while stored.

A 72v lithium-ion battery should be charged at least 30% before storing it for a good storage period.

How can you fix your 72v lithium-ion battery if it won’t charge?

If your 72v lithium ion battery does not hold a charge and discharges extremely fast, you should discharge your battery completely and then recharge it to its full capacity.

If it still does not hold a charge it means the cells are dead and refuse to hold a charge.

The only solution to this condition is to replace your 72v lithium ion battery with a new one.

How can you dispose of your 72v lithium battery?

Lithium ion batteries should not be disposed of directly as they contain hazardous material.

These batteries can be recycled but only at specific places.

The damaged or dead battery should be dropped at recyclable places or e-waste collection centers so that safety is assured as well.

About TLH Battery

TLH Battery Has been the number one leading lithium-ion battery manufacturer for over 15 years.We are focusing on custom battery pack solutions for industries.

TLH Battery owns three international service centers in United Kingdom, America, and Germany. helping you address your troubles and quality issues.

Everything you need to know about e-bike batteries [from a battery engineer]

Would you be the person taking the stairs or the escalator?

I’ll be honest. barring the one-off day that I’m feeling particularly sprightly, I would just hop on the escalator with those 30 people on the right. And I’m willing to guess that most of you would too.

What we can gauge from this picture is that most people would rather do as little work as possible to get from point A to point B. This is especially true when it comes to commuting on a bike. The picture above is analogous to the difference between a regular bike and an e-bike.

Even if we address all the concerns when it comes to biking in a city (like safe biking infrastructure), we can’t expect to change fundamental human behavior. when given the option between less work or more work to achieve the same outcome, people will more likely choose to do less work.

Since getting my e-bike, I can comfortably bike from my home in Somerville to the Seaport district in Boston. a roughly 5-mile trip. in just about 20-minutes. All of a sudden, biking 5-miles is a piece of cake. I also don’t have to spend time sitting in traffic, waiting for public transit, or worry about showing up to a meeting looking like I swam across the Charles river to get there.

The beauty of an e-bike is that it makes cycling an inclusive mode of transportation because it doesn’t discriminate by age or physical ability.

When it comes to purchasing an e-bike though, there are a plethora of options for both the bike and battery. So how do you decide which one is best for your needs? As a battery engineer who has built hundreds of batteries and logged way too many hours soldering battery packs, here are my thoughts on the most commonly asked questions when it comes to e-bike batteries.

If you’re new to battery terminology, you might want to start here: Battery terms that every e-bike owner should know.

In this post, we’ll cover the following questions:

What is the best e-bike battery?

This is one of the hardest questions to answer. There are so many variables that go into what makes a good battery and what’s best for you, may not be the best for me. Even then, a good battery can perform poorly if it’s not cared for properly.

Battery packs are made up of individual battery “cells”. Cells are classified into cylindrical cells (like your AA and AAA) and prismatic cells (like the one in your phone). Each class of battery is manufactured in a variety of form-factors (in the battery world we use this term to mean size). The most commonly used form-factor of cells in an e-bike battery pack is the 18650.

A battery pack is only as good as it’s weakest cell.

When it comes to batteries, in my experience, there is a strong correlation between price and quality. I don’t follow this rule when it comes to most things like for example, box wine (I’m just saying, there are plenty of really good box wine options these days!). When it comes to batteries though, you really don’t want to be compromising on quality because you’ll eventually end up having to pay the price.

Here are some things to keep in mind when purchasing an e-bike:

Cell Manufacturers: Panasonic, LG, and Samsung have a good reputation in the battery industry for their high quality cells, so paying a premium for these cells is certainly worth it. If the e-bike you’re trying to buy doesn’t have or provide cell manufacturer information, they’re likely not going to be a reliable source anyway.

Cell Chemistry: Lithium-ion (li-ion) batteries are the best option for e-bikes. Although lead-acid batteries are significantly cheaper, they’re three times as heavy as their li-ion equivalents.

Li-ion has several variants of cell chemistry. The most popular ones for e-bikes are Nickel Manganese Cobalt (NMC), Lithium Cobalt Oxide (LCO), and Lithium Iron Phosphate (LFP). The metrics to look for when selecting a cell chemistry are:

  • Specific Energy: has an impact on the range of your battery.
  • Specific Power: how the battery handles high load scenarios like going up
  • a hill.
  • Safety: does the chemistry have a history of high in-field failures.

There are trade-offs when choosing one chemistry over another, but as we’ve shown in the image below, NMC and LFP are both great options that both offer the best value in terms of performance, price, and safety.

Picking the right battery chemistry has to do with figuring out what matters most to you. Do you want a battery that has a longer range (higher specific energy) but doesn’t have as much power? Or do you want a battery that has a more power (higher specific power) but may not last as long?

In my opinion, the best e-bike batteries are likely going to be made from cells manufactured by Panasonic, LG, or Samsung with either LFP or NMC cell chemistry.

What is the range of an e-bike battery?

The range of a battery pack depends on the amount of energy packed inside of it and is measured in Watt-Hours (Wh). Watt?

Watt-hours are calculated by multiplying the battery capacity, in Amp-hours, by the battery Voltage, in Volts.

Let’s assume that, on average, 1-mile requires about 25Wh of energy. So a 14Ah, 36V battery should get you about 25-miles per charge.

Keep in mind that the weight of the rider, outside temperature conditions, and the amount of pedaling will make a significant difference in range.

A word of caution: the range that e-bike manufacturers provide should be taken with a grain of salt. That number is generated from tests that are run in perfectly tailored lab conditions. Do you charge any of your electronics in an incubation chamber set at 28° C with a lab-grade charger that applies the perfect current while charging? Yeah, I don’t either. And so, We should assume that the manufacture-specified range is delivered only if the battery is charged and discharged under ideal conditions i.e. not real world conditions.

For a more realistic estimate, shave off 15% of the manufacturer specified range and assume this padded number to be your real range.

If you’re looking for a longer range, choose a battery that has higher capacity (Ah). If you’re looking for more power, choose a battery that has higher voltage (V). Learn more why voltage and capacity matter.

What is the lifespan of an e-bike battery?

There are several factors that affect the lifetime of a battery such as:

  • environmental conditions: temperature during charging discharging
  • charging rate: how fast or slow your battery is charged
  • charging voltage: what voltage the battery is charged to
  • depth of discharge (DoD): what voltage the battery is discharged to

The list above isn’t exhaustive but, in general, batteries decay as a function of time in the charged state. Period.

Day 1: You get your new e-bike and charge it up to 100% and go on a bike ride. When you come home, you charge the bike back up to 100% and you’re excited to ride it again soon.

Day 2. 364: Life get’s in the way and you still haven’t been out on your bike since that first ride.

Day 365: One year later, it’s the perfect day for a bike ride and you finally have some time on your hands. You head to your basement, unlock your bike, and excitedly turn it on. 80% charge. What? You clearly remember charging your bike to 100% last year before moving it to the basement!

The truth is, we can’t beat thermodynamics. I’ll say it again: batteries decay as a function of time in the charged state.

bu-302, series, parallel, battery

Now, because you left your battery at 100% for a whole year in a basement with no temperature control, you inadvertently caused your battery to lose a certain amount of irreversible capacity. Your range will be ~20% lower and you’ll likely have to replace your battery sooner than you expected. The table below shows you how much recoverable capacity exists in a battery after storing it at different temperatures and different charge states for 1-year.

This is why a lot of electronics come with batteries that are only partially charged. to help slow down this decay. That being said, it’s hard to track how long e-bikes and their batteries have been sitting in warehouses before being delivered to your door so you could get a battery that has been decaying for a year or two.

Manufacturers also tend to overrate their batteries and will make claims about certain batteries having a lifetime of at least 1,000 cycles. Show.me.the.data.

The lifetime of a lithium-ion battery is described as the number of cycles until the capacity (Ah) drops below 80% of it’s initial capacity. In general, this is roughly 250-400 cycles (depending on battery chemistry and other factors) which amounts to roughly 1.5 to 2 years if you charge discharge daily and care for your battery properly.

How to charge your e-bike battery to make it last longer

  • The thing that will kill your battery faster than anything else is leaving it charged at elevated temperatures. If it’s 80 degrees outside and you have your e-bike fully charged, move it indoors where it’s cooler and try to drain the battery as soon as possible.
  • Charge your battery at room temperature as often as possible.
  • When sourcing an e-bike battery charger, the slower the charge rate the better. For example, if you have a 2-Amp charger, and your battery is a 14 Ah battery pack, you are charging at 14 Ah / 2-Amps = 7-hours. This is a nice, slow charge which will certainly improve the longevity of your battery pack. Avoid charging at rates that are faster than 2-hours for a full charge.

There’s a lot that goes into choosing the best battery for you e-bike, and there certainly isn’t a one-size-fits-all approach. But if I were buying an e-bike battery today, here’s what I’d do: LFP or NMC, slow charge, avoid storing or charging in hotter temperatures, and leave the battery at around 30% charge if you don’t plan on using it for a while.

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