Guide to e-cycle batteries

Cyclist on an e-cycle in Manchester for Cycling made e-asy
If you own an electric cycle or intend to buy one, here’s some advice from Richard Peace to help you choose the right battery, prolong the life of your e-cycle battery and save money at the same time

What kinds of e-cycle 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 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 undoubtedly 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.

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-cycle with a high-quality electric drive system as this helps ensure the batteries have been assembled to a high standards. Well-known drive-system makers include Bosch, Brose, Fazua, Mahle, Shimano and Yamaha. All these manufacturers keep close control of the batteries used in their systems – in the vast majority of cases they will be own-brand batteries.

Guarantee small print

Remember to check out the particular terms of the battery guarantee.

Shimano’s e-bike batteries (select the battery capacity section) are guaranteed by charge cycles (full charges, so two charges of half the battery capacity would equal one full one) – at least 60% of capacity is guaranteed to remain after 1000 full charge cycles. Riese & Muller guarantees that the Bosch batteries it uses will still have a capacity of 60% after two years or 500 charge cycles, depending on which happens first.

Your dealer should be able to determine the remaining battery capacity for you. 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 and also causes fewer problems on e-bikes with smaller wheels, as the weight of the battery sits nearer the ground. If ridden heavily loaded the extra weight at the top and rear of the bike can start to affect handling, though.

Rack-mounted batteries are found on some good-quality budget e-bikes, however, and shouldn’t be discounted. Gazelle’s Paris C7 HMB is one good example.

Downtube-mounted batteries are still very common, but are slowly being overtaken by frame-integrated batteries. It’s somewhat ‘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.

The tide certainly seems to be moving in favour of frame-integrated batteries, with many budget brands and online discount sites even selling such models, where once upon a time they were only to be found on premium-priced e-cycles.

What capacity do you need?

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

Battery capacity is measured in Watt-hours (Wh) and 400Wh, 500Wh and 625Wh are fast becoming standard sizes. In 2022 Bosch announced its biggest battery yet: a 750Wh frame integrated model to be used only with its new ‘Smart’ system. Note that this battery is not backwards compatible, even though many earlier batteries were interchangeable.

You might want to go small, though. For example, on an extremely lightweight efficient e-cycle or a folding bike that needs regular lifting, to keep the purchase price down 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 198Wh battery.

E-folders often use smaller batteries to keep overall weight down and keep them portable. The new Brompton Electric 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 up to a massive 1250Wh 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.

A handful of brands have developed ‘range-extender’ batteries – smaller batteries that clip onto the bike frame ready to feed their power to the motor. Specialized has been using such a system for a few years on its lighter e-bikes, the Turbo SL range.

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).

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 lets 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 has 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.

Conversely, an e-MTB ridden on high power settings over very challenging off-road terrain with a heavy rider could easily return a range of fewer 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. 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

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 and store the battery indoors in very cold or hot weather; avoid keeping them in direct sunlight.
  2. If you are riding all year round and often in sub-zero temperatures it could be worth getting a battery cover. Fahrer makes a variety of covers from neoprene and cordura.
  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-cycle in the first place they are more likely to have reliable battery management system (BMS) 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 long periods of storage as lithium batteries degrade slowly; but surely over time, whether used or not. If you do need to store one for a period of months, check what the maker’s recommended discharged state is for storage. For example, Bosch says that a charge status of approximately 30-60% of full charge is recommended for its batteries and that they are ready for use when they come out of storage.

End of life

Good-quality batteries are now more reliable than they have ever been. But even the best ones suffer a gradual decline in capacity over the years and so the range may eventually diminish to the point where it is unusable.

There three broad options if you need to replace a battery:

  1. Replace under guarantee. This only really covers the situation if a fault develops – a good-quality lithium ion battery should last more than a couple of years if used properly, two years being an industry standard for a reasonable length battery guarantee.
  2. Replace by purchasing a new one. If a battery is out of guarantee and at the end of its life then the industry advice is to replace it with one that comes from the same manufacturer and is of exactly the same spec. This is because battery, controller and motor have all been designed to work safely together and using a ‘non-original’ replacement pack introduces the potential for things not working as they should. Unfortunately, there are no common interconnectivity standards across the e-bike battery industry, with a multiplicity of computer chips and connectors used. One upside of total replacement is that you may have the option to upgrade to a larger-capacity battery from the same manufacturer.
  3. While option 2 may be the ideal and is certainly the ‘official’ advice, there are an increasing number of e-bikes around that are many years old and for which the original battery is no longer made. There may be third-party batteries available for the commoner makes of e-cycle battery that you could buy off the shelf.

Recelling by an expert company may be an option. This is certainly the case in continental Europe where e-bike use dwarves that in the UK and where e-bikes have been around in large numbers for much longer, giving rise to a second-hand battery industry where a number of expert companies can supply replacement batteries or recell your old one.

In the UK the industry is younger and there are less expert companies around. They do exist, though, and London’s eBike Batteries often gets good feedback. 

However, official industry advice is not to go down this route: non-expert, incorrect recelling or repair of a battery is most certainly a fire safety risk. However, there will be an increasing need for this service as the number of second-hand e-cycles whose original batteries are no longer made will increase dramatically over coming years and replacement batteries will be needed to avoid scrapping an otherwise perfectly good e-bike.