Ebike batteries in parallel. What is the best e-bike battery?


The two batteries you want to combine, and your ebike’s controller’s input, must all use XT60 connectors. If they do not, you must adapt them.


Connection Type: XT60 Connectors

Amperage Rating:

Must create a 1 inch air gap around device for cooling and understand risk involved

Input Voltage Ratings: 36-72Volt


While it may sound simple, adding a second battery to your ebike is a major challenge. Connecting them in parallel can be is EXTREMELY dangerous. If the batteries aren’t charged exactly the same you risk permeant damage that is not repairable.

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The Battery Blender solves this: You can now combine any two batteries of 1)different chemistries 2) different voltages 3)different outputs. The device will manage everything and protect your ride.

When using two different voltages, the Blender will “burn” charge from the higher voltage battery first, then engage the 2nd battery when within the lower voltage battery’s charge. As a result, it is important to turn off the higher voltage battery when it gets to a low level!

For example: If you combine a 52V and 48V Battery, the Blender will accept charge from the 52V only, until 54V is reached. From there, both batteries will output until 43V together. After 43V, only the 48V will be able to put out charge until 40V is reached. As a result, we recommend manually turning off your 52V if it does not have an intelligent BMS.

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Possible combinations with Bosch DualBattery

With DualBattery, a Y-cable splits the connection between motor and battery. In this way, both batteries are recognized by the energy management system and their capacity is combined. This now works with all current Bosch motors and batteries. Due to the numerous potential configurations, you have a lot of options. Depending on which batteries you combine with each other, you can achieve a total capacity of up to 1,250 Wh. You can choose from the Powerpacks with 400 and 500 Wh, as well as from the new Powertubes with 400, 500 and 625 Wh.

Does not fit every bike

Not every ebike is equipped with DualBattery right from the start. In addition, not every manufacturer offers a suitable kit for retrofitting it. However, the upgrade can also be quite easily installed by yourself. The biggest challenge is to properly attach the additional battery to the frame. This calls for a bit of creativity.

In theory, DualBattery works with all Bosch motors. In practice, however, the manufacturer of your ebike may have prevented this option for various reasons. This is not always the case, but it is possible. In most cases, the design of the frame simply does not offer enough space to integrate a second battery. Those who still want to try this out are thereby responsible, and in any case risk the warranty of the bike. Usually, a short message to the manufacturer is enough to find out what is feasible and what is not. Unfortunately, there is no list, database or similar, to help you safely clarify this by yourself.

The crucial question of space

If the signs are green, you can start. You will soon find out which spare parts and cables you need. First, you need to check one basic requirement: How much available space do you actually have.

Measure the available space in the frame of your ebike. There is usually space for the second battery on a frame tube, on the luggage rack or in the down tube. The last option is usually the ideal one. Depending on the type of bike, you will quickly find out how to best implement your project. E-cargo bikes usually offer several options. With a Fully E-MTB, or generally an ebike with a rather small frame size, there is a significantly higher risk of already giving up at this stage.

Dimensions of Bosch PowerTube: Bosch PowerTube 400 Wh: 360 x 84 x 65 mm Bosch PowerTube 500 Wh: 365 x 84 x 65 mm Bosch PowerTube 625 Wh: 428 x 84 x 65 mm

Dimensions of Bosch PowerPack: Bosch PowerPack 300/400/500 Wh Active and Performance: 325 x 92 x 82 mm

Dimensions of Bosch PowerRack: Bosch PowerRack 300/400 Wh Active and Performance rack: 372 x 76 x 122 mm

E-Bike Batteries: Volts, Amps, Watt Hours Explained

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What Are These Volts, Amps, and Watt-Hours? How Battery Specifications and Capacity Equate to Capability and Cost

Understanding e-bike batteries can be challenging, even for those of us in the know; the nitty-gritty details are figured out by electrical engineers with years of education and experience under their collective belts – and for good reason, it’s all chemistry and math over there!

You’ll encounter a host of terms when reading about e-bikes or looking at electric bike battery specifications: things like battery size, capacity, voltage, amp hours and watt hours. Some of these words are more-or-less interchangeable, others are related but distinct. All of them can be confusing, but they are also hugely important in understanding electric bikes and their capabilities – most notably when trying to interpret how far they can take you before needing to be recharged.

In this guide to e-bike batteries, the helpful writers at Electric Bike Report will help you to understand the meaning of common battery terms and their relation to the performance of the electric bikes they power.

E-Bike Batteries Explained

Batteries are one of the core elements of electric bikes. They are needed to supply power to the motor, which in turn provides assistance to the rider, and reduces the amount of human effort needed to move the bike.

E-bike batteries come in various sizes, and can be mounted to the frame in different ways. Some are fully internal, and are sealed inside the bike’s frame. As such, they are not removable, except by using special methods and tools available to professional technicians. Others are removable for easier charging and replacement, whether mounted completely externally (outside the frame), partially recessed (sunken into the frame to some degree), or completely recessed (sunken entirely and nearly invisible on the bike).

Regardless of their type, all e-bike batteries are actually battery packs, and are made up of groups of cells, similar to the standard AA or AAA batteries used in everyday applications. The number of cells and the method used to cluster them together determines how quickly they can provide power and how long they can continue to supply it.

In contrast to standard AA or AAA batteries, however, those used in e-bikes are most commonly rechargeable lithium-ion batteries similar to those used inside smartphones and in conjunction with cordless power tools. Lithium-ion batteries are efficient and can be recharged hundreds or even thousands of times if cared for properly. The Light Electric Vehicle Association, or LEVA, has a great article that they allowed us to re-publish regarding proper battery care and safety to ensure maximum life span.

Fully integrated batteries such as the one on the Velotric Nomad 1 can match the bike’s color and disappear into the frame.

Electric Bike Battery Terms and Definitions

Before we dive deeper into the details, let’s consider a couple of examples of e-bike battery specifications in relation to how they usually appear:

V = Volts and Ah = Amp-hours

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V = Volts and Wh = Watt-hours

Both examples convey two basic measurements, albeit a little differently. In both examples, we see volts first; this measurement relates to the availability of the electrical energy the battery can deliver. Next, either amp-hours or watt-hours are shown; these represent a battery’s capacity, or the amount of power it can store.

Let’s define these words (and a few helpful additional terms) a bit more clearly:

Current: the flow of electricity, or transfer of electrons, through a circuit.

Circuit: a closed system of wires and electrical components through which current can travel.

Volts (V): the amount of electrical force or pressure the battery can produce; the speed of the battery’s output of current. This is also sometimes referred to as the electromotive force, and is more specifically the speed at which electrons move through the system.

Note that this is a nominal rating that is used for classification purposes. In reality, a battery’s voltage varies based on the amount of power being drawn from it at a given moment, as well as the battery’s present level of charge. As current is drawn from the battery, its voltage decreases. This can be seen in an e-bike battery voltage chart.

Voltage is determined by the number of battery cells arranged “in series”.

Amps or amperes (A): a measurement of the strength of the battery’s output, or current. specifically, the volume of electrons passing through the system. This is limited by the size of the wires making up the system. Larger wires allow more current, smaller wires allow less. Generally, systems with higher voltage should use smaller wires (that limit amperage) to prevent overheating.

Amps can also be thought of as the amount of energy being drawn from the battery by what it is powering, and can fluctuate from moment to moment. In the case of e-bike batteries and their motors, a greater number of amps are drawn as the motor works harder (i.e. going uphill or using only the throttle).

Amp-hours (Ah): a measurement of charge; the amount of energy that can be delivered through an electrical system over the course of an hour.

In the case of a 10 Ah battery, it can deliver 10 amps of power in one hour, or 1 amp of power for 10 hours, etc, depending on the needs of the component that is delivering power to.

Amp-hours are determined by the number of clusters of battery cells arranged “in parallel”.

Watts (W): a unit of power, determined by volts and amps; the amount of work that can be done by one amp of current delivered at 1 volt. The amount of work is determined by the rate at which the energy is used.

This measurement is generally applied only to an e-bike’s motor, but its battery must support the motor’s needs.

Watt-hours (Wh): another measurement of capacity. In this case, the amount of work that can be done, or the amount of power that is spent, over the course of an hour. This is a direct result of a battery’s voltage multiplied by its amp-hours.

As such, a 24V, 20 Ah battery and a 48V, 10 Ah battery might look different on paper, but they have about the same amount of energy. This makes watt-hours a more reliable indicator of capacity when comparing different batteries.

Controller: A device that limits the flow of electricity through a circuit, and prevents a battery from discharging its energy all at once. In terms of an electric bike, this is the “brain” that adjusts the pedal assist system, the amount of input the motor contributes, and the e-bike’s speed.

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.

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.

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

Also, subscribe below for alerts on our next post to learn more about batteries!

You’ll Always Be Prepared

Life happens, and it’s always best to be prepared. When you have a second battery, you’ll be ready for whatever happens. Your e-bike unexpectedly runs out of juice? No problem, just swap it out for the second one. Your first battery won’t turn on? Unfortunate, but you’ll still be ready to ride with your other battery. You misplaced your battery? The second one is ready to go! And when your battery finally reaches its end of life, around 60% of its capacity, you’ll already be prepared with your back-up battery.

Over the years, battery technology has gotten better and with that, batteries have become less expensive to make. Now is the time to buy a second battery if you’ve been mulling it over these past few years but haven’t had the extra cash. And right now, during our Battery Sale, you’ll save even more. Now through February 13th, you can get a Juiced Bike Battery for 599, that’s 200 in savings!

A second battery is a great option for e-bike riders at any level. It helps you increase your riding range, allows you to charge less, ensures you’re prepared for anything, and lets you save some money. Don’t miss out on our Battery Sale where you can purchase a 52V/19.2Ah battery for just 599 for a limited time.

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