The battery for your electric bike is typically worth about a third of the value of the entire bicycle, so it’s important to find a good quality one and take care of it
No matter what electric bike you buy nowadays, chances are it runs on a lithium-based battery. Believe it or not lithium batteries have been around since 1912 but it’s only been in the last 15 years that they caught on and became economical in consumer applications. There are “lithium-ion” batteries and “lithium polymer” (aka “lithium-ion polymer”) batteries and the difference between them is the type of electrolyte used. Other than that, there isn’t a significant variance: Li-Polymer allows for a slight increase in energy density but is 10-30% more expensive and so manufacturers have yet to decide upon one over the other.
There is also a range of lithium chemistries available in different batteries and manufacturers might claim some are more robust than others but the single most important factor affecting the life of a battery is how well it is looked after. You should typically expect a battery to last between 2 and 4 years if it is well maintained. (A lithium battery will slowly lose its capacity over time, even if it’s not used.) Below are three things you can do to ensure you get the longest usage out of your electric bike battery.
#1. KEEP THE BATTERY COOL
Environmental conditions are an important factor affecting lithium batteries. For example, leaving one in your car in the hot sun will guarantee you lessen the life of your battery. In fact, that would be the worst situation: keeping a fully charged battery at elevated temperatures. It’s a good rule of thumb to store your bike out of the direct sunlight for long periods and when not in use, keep your battery in a cool place, preferably below 20°C (68°F).
#2. STORE A BATTERY PARTIALLY CHARGED – BUT NOT TOO LOW!
You’ll also notice in the above chart that storing a fully-charged battery has an impact on the recoverable capacity. Even more important, storing a fully depleted battery may be disastrous because, as we mentioned above, a lithium-ion battery will slowly discharge over time even when you’re not using it. If the voltage drops below a certain point this may cause irreparable cell damage, depending on the time it’s left sitting. Ideally, when storing the battery for a long period, ensure it has a charge between about 80% and 40% of a full charge. Some chargers have a lower ‘storage’ voltage setting, so just switch to this before charging it for storage. An easy alternative is to take the bike for a ride after you’ve charged it fully and before storing.
Also, don’t leave your battery on the charger for long periods of time, as storing it at or close to 100% will reduce the life of the battery. You can also check your battery every couple of months over winter. If you notice that the battery indicator has dropped too low, you can give it a quick charge to bring it back to the ideal storage voltage (this is unlikely to be needed if the battery was at 40% or above). If you don’t have a battery indicator, it’s probably a good idea to charge the battery for half an hour every few months. Again, try not to put the battery away fully charged (but it won’t be the end of the world if this happens.)
#3. DON’T REGULARLY FULLY DISCHARGE YOUR BATTERY
It’s amazing that we still see tech sites advising regular full discharge of your battery, even when this has been proven as detrimental. Regularly discharging lithium-ion batteries to 0% is harmful and partial discharges with regular top-ups are recommended to extend the recharge-cycle lifespan of the batteries. The occasional full discharge on that extra long ride is no problem! It’s ok to top up lithium batteries regularly and, as the chart below shows, it’s best to operate them in the top half of their discharge cycle; lithium batteries don’t have a ‘memory effect’ that some other battery chemistries have. If you are doing short rides on a regular basis, it is slightly better to charge it every few rides rather than every ride (to avoid long periods at or close to 100% charge, as discussed above).
As an extra note for the winter season, make sure your battery is above freezing before charging, otherwise you could harm the cells. It is no problem to ride the bike in below-freezing conditions (it doesn’t harm the battery), just make sure you let the battery warm up before charging. When you are riding in very cold weather, you will notice a drop in power and range; this is normal and expected. You can help avoid this by bringing the battery inside whenever you aren’t riding to keep the temperature of the battery up. That way you will get that extra bit of power!
Correct maintenance and storage of your battery as detailed above will significantly increase its lifespan. A well-maintained lithium battery will last between three to five years, whereas a poorly maintained battery can be badly damaged over just one season or sooner. For more detailed, scientific information on batteries and how to care for them, check out the excellent online resource at Battery University, for more detailed information.