Lithium-ion batteries are the most widely used type of rechargeable battery in portable electronics, electric vehicles, and electric bikes. The batteries are powerful and easy to use, but expensive. For ebikes, the battery pack is often the most expensive component on the bike, so it is important to know how to best maintain and care for your battery. Here are a few things to keep in mind.
Compared to older lead acid batteries, lithium-ion batteries are energy dense. This means that they weigh less and take up less space for the same amount of power output.
Some older rechargeable batteries also had a memory effect. A memory effect refers to a battery “forgetting” its total charge capacity. When a memory effect was present, it was best to fully discharge your battery and recharge it back to full capacity for each charge cycle. This is not an issue with lithium-ion batteries, so it is safe to partially discharge your battery and then top if off after each use. This makes them ideal for use in ebikes.
During a battery discharge cycle (when the battery is being used), there are chemical reactions involved known as oxidation-reduction reactions. These reactions are parasitic, meaning they lead to inefficiencies and loss of performance over time. The two most important factors impacting the rate of these parasitic reactions are temperature and time spent at maximum voltage.
At warmer temperatures, the rate of parasitic reactions is increased, resulting in less overall range per charge. Ideally, batteries should be used at room temperature and stored at room temperature. We do not always have the luxury of riding at room temperature, but we can often control the temperature at which we are charging our batteries. So if you live in a warm environment, it is best to charge your battery inside your home away from heat sources and out of direct sunlight. Whenever possible, avoid storing your batteries in excessive heat.
Charging a battery to full capacity, or full voltage, also increases the rate of these reactions. For this reason, it is best to not leave your battery at full charge for extended periods of time. You can achieve this by not charging your battery to full capacity, or by making sure you use the battery fairly soon after charging to full. Leaving a battery at full charge for a day or two is not an issue, but you want to avoid leaving a battery at full charge for weeks and months at a time. If you do need to leave your battery unused for extended periods of time, leaving the battery around 50% of its maximum capacity is a healthy range to limit the rate of parasitic reactions and increase the lifespan of your battery.
Just as you do not want to leave a battery at full charge for long periods of time, it is absolutely critical not to leave your battery completely depleted for long periods of time either. The reason for this is that the battery management system (BMS) needs to draw some energy at all times to monitor the internal state of the battery. The BMS will turn your electric bike off before it drops below an unhealthy voltage, but if it is not recharged soon after this, the continuous draw can drop the battery below a healthy voltage. As a safety precaution, the BMS will then not allow the battery to be recharged. At this point your battery is unusable and will need to be replaced.
Your battery manufacturer tests the ideal rate to recharge their battery, so it is recommended to use the charger that comes with your battery. Fast charging or supercharging involves more heat than slower charging methods. You want to avoid excessive heat when possible, so if you have time to slow charge your battery, you are going to extend its lifespan.
To summarize, avoid excessive heat, do not leave your battery at full charge for extended periods of time, recharge your battery anytime it discharges completely, and use the charger that comes with your battery. If you follow these few steps, you will take full advantage of one of the most important components of your ebike.