The battery is what gives energy to the motor, and constitutes the single most expensive item to be found on a typical ebike. There are many different kinds of ebike batteries. In general, cheap batteries are heavy and offer only a small range; as the price goes up, so does the range, while the weight goes down. A quality battery moreover lasts for longer (that is, for more recharge cycles), and therefore you will need to change it less frequently.
Ebike batteries can be divided in three main groups, according to their chemical composition:
- Lithium-ion batteries (Li-ion): at the moment, this is the best technology among those used to produce ebike batteries. They are much smaller and lighter than other kinds of batteries, with a typical capacity of 90-150Wh per kg. This means that li-ion batteries are lighter and have a bigger capacity than equal-sized lead batteries. Moreover, li-ion batteries do not suffer from the “memory effect”, that is they can be topped up any time you choose. As you can imagine, the down side is that they usually carry a higher price tag, due also to the more complex electronic battery management system (BMS). This is the kind of battery that we advice you to choose, as the higher initial price is compensated by a better performance and a farther “best before” date.
- Lead batteries: this is the oldest techonology still in use for rechargeable batteries. Their weight/range ratio is bad, meaning that they are very heavy for the kind of capacity that they offer (about 25 Wh per kg). Recharge times are longer, typically requiring 8 hours or more. Choose a bike with this kind of battery only if you want to save as much as you can on the initial price, but prepare for a poor performance and be aware that you may have to substitute it after a year or less.
- Nickel-metal hydride batteries (NiMH): these are better than lead batteries, but fall still quite short of the li-ion batteries in terms of capacity per kg (about 55-70 Wh per kg). They suffer more from a self-discharge effect (meaning that they tend do discharge fast even when not in use), and suffer from the “memory effect”, which reduces the capacity of the battery in case of partial charge and discharge cycles. Nowadays only few ebike models use NiMH batteries, and we suggest you avoid them.
Sometimes ebike producers offer the same ebike in two variants, with batteries of different quality. The difference in price between an ebike with a lead battery and an ebike with a li-ion battery can be about 250-300€, or even more.
Ebike battery capacity
A very important factor to help you decide which ebike to go for, is the capacity of its battery. The capacity, measured in Watt-hours (Wh), is directly related to its range: the higher the Wh value, the farther you’ll be able to travel with your ebike. Please refer to our page on ebike range for a fuller discussion.
A Wh is equal to the value of Ampere-hours (Ah) of a battery, multiplied by the Volt (v) of the battery. A typical 36V, 10Ah battery has 36×10= 360Wh.
How to manage the battery of your ebike
Batteries are usually the single most expensive component of an ebike. It is therefore important to learn how to manage them best, in order to prolong their lifespan.
A few general remarks: it is important to understand that ebike batteries are indeed rechargeable, but only up to a point. As the months and years go by, their capacity slowly diminishes, until it is time to substitute them. With a typical use of your ebike, and a careful management, a li-ion battery will last about three years.
Batteries work at their best at the same temperatures that humans do. When it’s cold (below about 10°C), you should keep the battery inside, in heated rooms, as much as you can, and also recharge it at room temperature; you should take your bike outside only when it is time to actually use it.
Batteries may be damaged also when they are often overcharged. Modern electronics control system should be able to reduce the voltage from the charger once the recharge is complete, but you should all the same disconnect the battery from the charger as soon as it is fully charged. Batteries, especially li-ion ones, may be damaged as well when they are fully discharged. If, for instance during the winter months, you don’t use your ebike, you should anyway regularly recharge your ebike battery, at least once a month.
Finally, ebike batteries must be treated with care: try to avoid dropping them or exposing them to vibrations, as the chemical components within them may be damaged.
Read this article on a test on ebike batteries to understand why they cost so much.