Building ebike battery pack. Step 3: Label your cells

Category: Battery Building Instructions

The 1s6p modules from Maker Batteries are great for building large capacity batteries. At just over 20AH each, a single series chain of modules can create a large 20AH battery pack. In this tutorial I’m going to assemble a small 12V 20AH pack, but you can build a larger 24V, 36V or 48V pack with these same instructions by simply adding more cells in series.

Step 1: Measuring each module’s voltage

To start, I’m going to lay out all of my modules and measure their voltages. They should all be within a couple hundredths of a volt. They were checked at the factory and again before shipping, but this is just a sanity check right before we build the battery to triple check that all of our cell modules are good.

Step 2: Laying out the cell modules

For these 6p straight modules, the number of different possible layouts is fairly limited. You don’t have as much creativity as with the triangular modules. The two major layouts are either straight packing or offset packing, demonstrated in the two pictures below.

Straight packing will give you a narrower but longer battery, while offset packing will make a wider battery with less total volume. This is because offset packing is more efficient by leaving less space between the cells. It also gives you twice as much surface area to apply the hot glue (each cell touches the next row in two places instead of one).

The difference between straight and offset packing doesn’t seem like much on such a small battery like this 12V pack, but when you get up to larger batteries like the 13 module 48V20AH battery kit below, offset packing can make a big difference in the length of your final battery.

Regardless of the type of packing you go with, remember that you’ll need to place every other module upside down in the pack so that you can easily solder the cell modules in series. Your pack should look like this, depending on the voltage:

Now you can go ahead and glue your cell modules together. Use hot glue liberally and make sure you’ve got a nice strong connection between cells. These packs start to get heavy as you add more modules, so make sure you’ve got a good glue joint to keep them together. If the glue joint happens to fail while you’re working on the pack, just shoot some more glue in the spaces between cells. Be careful not to short the pack later on with the metal tip of the hot glue gun though!

Cheap Li-ION ebike batteries

Cheap Li-ION ebike batteries cost less than a tenth of the price of brand name batteries of the same capacity. A common 36 volt, 10AH Li-ION battery pack sells for around US300 on Amazon where similar capacity batteries for brand name electric bikes are over 3000. Here’s the thing There is a trade off between quality and economy. Low cost replacement batteries are cheap for a reason. There are a number of issues with cheap ebike batteries: They are unreliable, frequently constructed incorrectly, rarely meet their claimed capacity rating, and are often dangerous. Despite the drawbacks, the relatively low cost of cheap batteries is compelling as brand name replacements are beyond the budget of most ebike owners. This raises the question:

Which batteries are best for ebikes?

For the past 20 years, the best ebike batteries have used Li-ion 18650 cells. Li-ion has dominated as the best technology and advancing chemistry continues to increase capacity and reliability. Li-ion provides the highest power for size. It is reliable, light and cost effective.

For the next few years, the electric vehicle world will continue to use Li-ion chemistry and Li-ion continues to be the best option for most electric bicycles.

If you want maximum power for your dollar then lead acid batteries are the best option. The issue with lead acid batteries is that they are over 4 times the weight of Li-ion equivalents. For electric bikes, the extra weight of lead acid batteries is a problem for most riders.

Many alternative battery chemistries have shown promise over the years. Lithium polymer (LiPo), Nickel metal hydride (NiMH), and Lithium Ferrous (LiFe) have all tried and failed to better Li-ion.

There is, however, massive investment in a range of new technologies which extend the range that electric vehicles can travel before requiring a recharge. The most promising technology that is beginning to emerge is rechargeable hydrogen cells. [click here to read our article on ebike batteries using hydrogen cell technology]

Rechargeable hydrogen cells are available now although they are in an early phase of production. In 2021, this very new form of powering electric bikes is beginning to roll out in Australia. Hydrogen cells for electric bikes would be expected to reach Europe and the US in 2022 if the technology proves to be successful.

As the roll out of cost effective hydrogen cells is new to the market, it is still too early to say whether they will begin a revolution in powering electric vehicles.

Ebike battery replacement

Once you have coughed up the substantial investment required to purchase your e bike, you typically have a year or two of good use before the battery supplied with the bike begins to fail. If you can afford a brand name ebike, you would typically expect the battery to last two to three years before the travel distance becomes annoyingly short.

It is a shock to most e-bike owners that replacement batteries for most ebikes can be more than half the price of a replacement bike with the latest battery fitted. In addition, the Rapid re-design of ebikes often means that it is difficult to obtain a replacement battery that fits your model bike.

When the battery dies, ebike owners are forced to seek a low cost replacement, or scrap the bike completely. The problem is that a good replacement battery by itself can cost as much as the e-bike with the battery included.

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!

building, ebike, battery, pack

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

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.

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.

Have questions? We’d love to help. You can get in touch using the contact form or find us on @somerville_ev

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What should I take into account in the battery of an electric bike?

The e-bike battery package can be built according to the user’s needs using high-capacity cells or high discharge cells. The most common need is to maximize travel, meaning we usually put LG MJ1 18650 cellsto provide 3.5Ah capacity per sensor. Another excellent, slightly cooler option is the Panasonic-Sanyo NCR18650GA 18650 battery cell,3.5Ah capacity and 10A discharge.

The lithium battery possible bms is also the hardest element in the battery. The BMS charge control circuits from the manufacturer have pre-programmed in-control. It involves not only monitoring battery performance, but also discussion sup with the bike management system. For example, the battery tells information about its charge to the bike’s driving computer, which requires much more complex programming. Of course, e-bike manufacturers do not sell separately BMS circuits, but directly from new batteries.

BMS is the biggest challenge for the do-it-yourself construction. The battery pack may keep the battery dead if it has been empty for a long time. Even if the cells are loaded separately back into a good reserve, the programming of BMS cannot usually be changed at home. In this case, you will need to buy a new battery or put in a generic bulkkiBMS that monitors the battery cells, but does not know how to do anything else. Then the electric bike can run on an old battery, but it no longer knows the same tricks as the original.

Do-it-yourself e-bike battery

Only BMS status is an obstacle to those who are handy with their hands. If the BMS is very awake in the battery, but the battery cells are tired, the cells can be replaced.

Here’s a good example for english speakers in the video:

The video makes 13S2P, or 13 cells in series, 2 parallel battery packs. It uses Samsung INR18650-25R 18650 battery cellsthat provide 20A continuous discharge current and 2.5Ah capacity. The parallel connection of two cell lines means 5Ah capacity and 40A discharge current in the battery pack. 13 cells in a stick, i.e. when connected in series, make the battery pack 13x 3.6V = 46 V.

What does it take to get a battery?

When building the battery pack, the battery cells must be as close as possible to each other. In the worst case, if the battery has a high voltage difference, you can build a battery that has not worked.

Connecting the batteries into a battery pack is done by spot welding. Spot welding is practically the only working way, as knocking heats the battery too much and at worst spoils the entire cell.

Spot welding supplies electrical current to the welding site, which provides the heat required by the weld. The result is a very neat welding result and the battery cell remains intact.

For more information on how to design and build your battery, see Visit at least check out the images.

Custom-made e-bike battery

If your battery is running out of time, you can also send it to us. We’re analyzing the potential for that condition and re-encapitsion. After the measurements, we agreed with the customer which direction to go with the project. We can order any battery cell from the battery pack, including the new 20700 and 21700 battery cells.

The cost of work consists of battery cells and work done. Depending on the complexity of the battery, the work can cost 150-200 euros. As a result, we’ll send back a battery that probably has better features than original ones. (No need to use the most cheap cells, so you can maximize, for example, the capacity of the battery size within the limits allowed.)

The cells of the e-bike batteries depend a lot on the battery structure and desired features, so please contact us by email info @

At least the battery model and preferably a picture of the battery should be attached to the message. Let’s build the batteries that are right for you!

You can send the battery to:

  • Jesi Verkkokaupat Oy
  • Pääskynlento 13 B 43
  • 20610 Turku, Finland
  • 045 263 8565
  • Don’t forget to bring the charger!

How much power and battery do you need?

Once you’ve chosen a kind of motor, you decide how much motor you want, as well as how much battery you want behind it. Motors have watt ratings, batteries have voltage and amp-hours—it’s a dense thicket for a newcomer. Micah Toll, an engineer who writes at and Electrek, helped me FOCUS on what matters.

First lesson: Ebike motor ratings are mostly nonsense. Some countries cap ebike motors: 250 watts in much of Europe, 750 watts in much of the US. Not coincidentally, motor makers and sellers advertise a motor’s “continuous” power instead of its peak rate. The more clear way to compare ebikes is to look at the voltage and current (amperage) for hill-climbing and top-speed power and to consider watt-hours for battery longevity.

You can tweak the voltage and current with different battery controllers, gaining more speed, more hill power, or different assist levels. The power you need depends on a lot of factors, including your body weight, the bike’s weight, and your pedaling power. Bicycling magazine has a deep dive on how to understand ebike motors and power (presented by Bosch, which makes its own ebike motors). Generally, Toll suggests, 24- and 36-volt setups are for casual riders who plan to pedal a good deal and don’t face lots of hills, while setups at 48 volts and above are useful for hills and no-pedal throttle riding.

I went (very) small for my wife’s roughly 650 ebike kit from a company called Leeds: a 250-watt, front-hub motor, powered by a 24-volt battery with 5.2 amp-hours, roughly the size of a squared-off 16-ounce beverage can. But watt-hours (Wh) offer a better battery comparison than amp-hours (Ah) do. You get watt-hours by multiplying the battery’s voltage (in this case, 24) by its amp-hours (5.2), so for my wife’s kit, that works out to about 125 Wh. Technically that means her fully charged battery can run her 250-watt motor at full power for about half an hour. It’s a useful comparison, but ebikes pull “full power” only during hill climbs and acceleration, so their batteries usually last much longer. On a paved-road commute, your legs can likely put in 100 to 200 watts of power on their own, so using a low-key kit like this is like having an on-demand tandem partner.

For such “assist” rides, 250 Wh is a better starting point these days, according to Toll. If you’re going to be riding your throttle most of the ride, 500 Wh (that is, a 48 V, 10 Ah setup) is your starting point.

If you want something close to an electric moped experience—almost entirely throttle, 25 to 28 miles per hour—you’re looking at a 750 Wh setup. At that point, you should be checking your local laws and also considering whether you ought to simply buy a dedicated ebike, because in terms of price, design, and safety, you’re likely better off with one.

My wife’s ebike is working well. Because she can safely store her bike at work and at home, she removes her battery only about once a week for charging. She gets most of the exercise of biking but can push a button to get a faster start at intersections or to tackle hills. It has made her more confident in biking around the city, which means the local bike shops still get some business in accessories, lights, and more.

Do you need to upgrade your brakes?

If you’re installing a lightweight battery and motor that you expect to use mostly as an assist to active pedaling, your current brakes may be fine. Disc brakes provide better stopping power, especially in wet conditions, but a good rim brake can suffice for commuting-focused rides. Toll said he spent three years riding a DIY 1,000-watt ebike with mechanical V-brakes (the kind you might see on a 10-year-old mountain bike), and it worked out well. “It’s more about the quality of the brake,” he said. At a minimum, though, check your brake pads and performance, or have a shop do a tune-up, when you’re installing a kit.

Many ebike kits and motors come with replacement brake levers, or sensors that can attach to your existing levers. These shut off the motor when pressed so that your motor stops pushing immediately when you mean to stop. I haven’t found them helpful on my own 250-watt setup (more on that in a bit), but there’s no harm in installing them.

Where should you buy a conversion kit?

There’s no one ebike kit that I—or anyone—can recommend for most riders and bikes. But Adam Ostlund, Micah Toll, and Karl Gesslein, ebike enthusiast and author at, all offered one bit of buying advice: Never try to “save money” by hunting for cheaper batteries. A cheap battery is almost always disappointing—and sometimes dangerous.

Bike batteries usually consist of a series of 18650 cells that are connected to one another and a battery-management system and then packaged into various shapes. Reputable battery makers and ebike-kit sellers use the best-quality cells from brand names like LG, Panasonic, and Samsung. In contrast, most discount sellers use lesser cells, from lesser-known makers, that have diminished capacity, voltage, and longevity, and their controllers can be equally suspect. Buy from a dealer with an established presence and return policy.

You can often find motors, batteries, controllers, wires, throttles, sensors, and other accessories sold separately, but unless you have a few conversions under your belt, you’re better off with an all-in-one kit. Kit makers have spent a lot of time testing how components work together, and they should be available for troubleshooting. Ostlund noted in our interview that Electrify Bike custom-programs some of its kit controllers so riders aren’t stuck with the often aggressive acceleration curves of some motors that are meant more for delivery workers than for weekend warriors.

Ebike-kit companies that were mentioned by the experts I talked to, are linked in ebike-enthusiast subreddits, and have generally built a good reputation include:

  • Luna Cycle (affiliated with and Gesslein)
  • Electrify Bike Co. (Ostlund’s shop)
  • Grin Technologies (batteries, motors, and kits)
  • eBikeling, Leeds, Hilltopper, Dillenger (hub kits)

What about Swytch kits?

Search online for ebike kits (or in the Комментарии и мнения владельцев posted on this article after its original publication), and you’ll see Swytch mentioned a lot. It’s a UK-based company, but it has a US warehouse for returns and distribution, as well as a one-year warranty on most parts. The company offers 250-watt, front-hub-based full conversion kits for bikes with 26-inch and 700c wheels, as well as for Brompton folding bikes. You have to preorder your customized kit, and you might wait a while, as Swytch prepares and ships kits in batches.

Swytch’s main hook is its unique battery and connector, which clicks on and pops off your front handlebars at the press of a button. Most people have room on their bikes there, and the design simplifies removing the battery when you’re locking up. Swytch recently announced the smartphone-ish–sized Air battery for those who value even more portability, and lighter weight, over range.

Swytch sent me a test kit for my own bike—a 2018 Norco belt-drive hybrid with 700c wheels—with a Pro battery (30-mile range) and both a cadence sensor and a throttle. After jumping on a video call to double-check my fork dropout width measurement (an important detail for any conversion kit), I ran the cables and installed the kit without much hassle.

building, ebike, battery, pack

My bike is already on the heavy side, and I’m biking for errands or recreation more than personal records, so the roughly 3 pounds of difference that Swytch’s motorized front wheel adds is tolerable. You’re more likely to notice the 4-pound battery on the handlebars, but that feeling soon disappeared for me—and so did hills, and starting on an incline, and feeling weighed down by cargo.

building, ebike, battery, pack

There are better ebikes for those committed to riding electric every time or for those interested in commuting longer (or steeper) distances with less pedaling, but I’ve enjoyed the versatility of the Swytch kit for weekend trips and weekday errands. If hauling a battery around will be a pain, or the ride is real short and my knees feel great, I can skip it. If I want a faster, smoother ride, I can grab the battery and head out. If bike space and versatility are a priority for you, the Swytch kit is worth considering.

If you’re unsure about any aspect of your conversion, look for your bike model on the Endless Sphere forum or the r/ebikes subreddit, or simply search the web for your bike name plus “ebike.” Bike owners who have stealthily converted their bikes into electric-powered dynamos love to tell people about it. Not that I’d know anything about that.

This article was edited by Christine Ryan.

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