A guide to e-bike batteries

Bosch dual battery system on a Riese and Muller e-bike
Bosch dual battery system on a Riese and Muller e-bike
Bosch dual battery system on a Riese and Muller e-bike

A guide to e-bike batteries

With electric cars not yet commonplace, e-bike batteries may very well be the largest and most expensive batteries you might find around a typical UK house. If you own an electric bike or intend to buy an e-bike, here's some advice from Richard Peace to help you choose the right e-bike battery, prolong the life of your electric bike batteries and save you money at the same time.

What kinds of e-bike batteries are there?

On new or recent e-bikes you invariably get some kind of lithium-ion battery. Older second hand e-bikes may have other chemistries; the earliest e-bikes featured very heavy lead acid batteries, then came nickel-cadmium and nickel-metal hydride, both of which were lighter and can still be found to retain a useful amount of capacity for shorter runs – perhaps useful if you are looking for a really cheap and cheerful second hand ‘hack’ e-bike. Giant’s Lafree model and some Heinzman kits were highly regarded at the time and still turn up second hand with these nickel based batteries.

However, despite the extra expense and complexity, a good quality, decent capacity lithium-ion battery is often the most practical option; it will give you the best range, reliability and longevity. You might read all kinds of claims for different variations of lithium-ion e-bike battery, with cobalt, manganese and more included in the mix. Don’t worry! There doesn’t seem to be any great expert agreement on which of these formulas is superior, so for now it’s more important to get a well made, high quality lithium-ion battery, regardless of the chemistry used. In practice this means batteries with cells (cells are the individual components of batteries) from reputable makers like Sony, Panasonic and Samsung.

Equally important is to buy an e-bike with a high quality electric drive system as this helps ensure the batteries have been assembled to high quality standards. Well-known drive system makers include Bosch, Brose, Shimano and Yamaha to name a few.

Guarantee small print

Also check out the particular terms of the battery guarantee. Shimano’s own brand e-bike batteries are guaranteed by charge cycles (i.e. full charges) – at least 60% of capacity is guaranteed to remain after 1000 charge cycles. Your dealer should be able to determine the remaining battery capacity for you. Riese & Muller guarantee that the Bosch batteries they use will still have a capacity of 60% after two years or 500 charge cycles (depending on which happens first). Note that a good quality battery is still able to be used at below 60% capacity – probably for a good few years, it is just out of warranty.

For a very approximate idea of your e-bike battery capacity you can try the home test method.

Rear rack, frame-integrated or frame mounted? 

There are three common mounting positions; rear rack, on top of the downtube or totally integrated into the frame.

The first option is OK for lighter batteries on lightly loaded bikes intended for more gentle riding. If ridden heavily loaded the extra weight at the top and rear of the bike can start to affect handling. Rack-mounted batteries are found on some good quality budget e-bikes however and shouldn’t be discounted. Raleigh’s Array model is one good example.

Downtube-mounted batteries are still very common but are slowly being replaced by frame-integrated batteries. It’s rather horses for courses which of these options you might choose.

Those mounted on top of the downtube can be less fiddly to get on and off the bike but integrating the battery into the frame gives more protection from knocks and looks more aesthetically pleasing to many. Downtube-mounted and frame-integrated give better handling than rack-mounted batteries as the weight is kept low and central.

What capacity battery do you need?

As a general rule it’s best to get the largest and best quality battery you can as this will mean an easier life for your battery (i.e. less charge cycles) and also more range per charge.

Battery capacity is measured in Watt hours (Wh) and 400Wh or 500Wh are fast becoming standard sizes. 

You might want to go small though, for example on an extremely lightweight efficient e-bike, folder or if you simply know you’ll only be making short trips. The Cytronex C1 system is a good example of a lightweight, efficient system that can achieve impressive ranges on lightweight e-bikes from its modest 180Wh battery.

E-folders often use smaller batteries to keep overall weight down and keep them portable. The new electric Brompton is actually one of the larger batteries found on a folder at 300Wh and neatly removes in a jiffy to help carrying.

Conversely, if you are after maximum distance on a single charge there are dual battery systems out there that mean you don’t even have to swap batteries. Bosch’s own dual battery system gives a massive 1000Wh capacity – enough to ride all day on high power settings – and it automatically draws power from both batteries at an even rate, the optimum method for giving your batteries an easy life.

Focus are e-bike manufacturers from Germany and use their own system dual battery system which gives 756Wh, used with the renowned Shimano motor system.

BESV have managed to cram 762Wh into a single battery – for example on their TRB1 Urban model.

How many miles will I get from my battery?

How long is a piece of string? A very rough rule of thumb is to divide the Wh capacity of a battery by 15 to give a very rough estimate of the range (for example giving an estimate of around 33 miles from a 500Wh battery).

Of course actual range depends on power level selected, rider weight, terrain and weather and can vary massively. Bosch’s Range Assistant is a useful guide to likely range as it let’s you estimate the effect of various factors on range, though I have always found it a little on the optimistic side.  

You can get many times more mileage than you might expect. For example Cytronex have reports of fit road riders using their system and getting 50 miles plus to a charge on a 180Wh battery - less than half the capacity of many standard size batteries. Similarly an e-mtb ridden on high power settings over very challenging off-road terrain with a heavy rider could easily return a range of less than 20 miles on a complete charge of an average capacity battery.

Tips for extending battery range include conservative use of the power settings and using the gears to keep the pedals spinning at a fairly fast cadence as well as moderating your speed; for example riding at 13mph instead of the max assisted speed of 15.5mph will usually save a good amount of battery capacity. 

How to look after and store lithium ion batteries for electric bikes

There are a few basic but important tips you can follow in order to keep your battery in tip top condition:

  1. Batteries have an optimum operating temperature - around room temperature. So charge the battery indoors in very cold weather, and keep it indoors until the last second to keep the cells warm. Keep the battery indoors in colder weather and avoid storing them in direct sunlight.
  2. If you are riding all year round and often in subzero temperatures it could be worth getting a battery cover. Fahrer make a variety of covers from neoprene and cordura – here’s a more in depth look at them.
  3.  All batteries will be damaged if persistently over-charged or over-discharged. Use the correct charger for your battery (in particular never use one that wasn’t specifically made for your battery). If you buy a good quality e-bike in the first place they are more likely to have reliable BMS (battery management system) units in the battery which also helps prevent over charging and discharging.
  4. Don’t leave a lithium battery connected after it has achieved full charge.
  5. Be wary of cheaper batteries with suspiciously high claims for battery life and the number of charge cycles they will last – it may have been set close to the limits for under and over charging which could lead to premature failure.
  6. Avoid vibration and shock to a battery through rough handling or careless treatment as this can lead to a shortened life too.
  7. Try to avoid storage as lithium batteries degrade slowly but surely over time whether used or not. If you do need to store a lithium battery for a period of months check what the maker’s recommended discharged state is for storage. For example Bosch say that a charge status of approx 30 to 60% of full charge is recommended for their batteries and that they are ready for use when they come out of storage.
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