If you dig around online, you will find many claims that only charging your lithium battery to 80% will prolong its life. While that is true to some degree, it is not the full explanation, and limiting the charge in this manner can also reduce the capacity of your battery.
In short, we recommend using only the original charger that came with your battery to ensure proper operation for the life of the battery.
For the longer explanation, it helps to understand that your battery is made up of many smaller cells. In the case of our Omega model, the battery is comprised of 39 cells, arranged in three groups of 13 to achieve the 48-volt nominal rating. Much like a chain, the capacity of a battery is defined by its weakest link. That is, if you have 38 cells that are in perfect health, and one cell that is at 50% capacity, the capacity of the entire pack will be 50%.
When you charge the battery, the battery management system (BMS) also balances all of the cells, ensuring that they all reach a full charge. Crucially, this balancing stage only happens at the end of charging, typically above 90%. When you only charge the battery to 80%, the cells never get balanced. Over time, they can drift apart from each other. For example, one cell may be starting from 50% charge while all of the rest of the cells are starting from 60% charge, so you will only be able to put 40% of a charge into that pack, and you end up with a battery that is only charged to 90%.
Think of your battery as an ecosystem, comprised of the cells, the BMS, all of the electrical connections, the outer case, and the charger. All of these components work together to provide you with the best performance from your bike. When you change one component, it can affect how all of the others work.
If everything else is equal, charging to 80% will extend the lifespan of your battery. That said, the only way for this to work is if your BMS is set up to balance below that point. None of the batteries that we sell includes a BMS that can work with an 80% charge and still balance the cells. For this charging strategy to be successful, you would still need to use the original charger frequently to ensure that the cells stay balanced.
In practice, this is something of a red herring. The unfortunate reality is that your battery is likely to die from time long before it ever wears out from usage. The expected lifespan of a lithium-ion e-bike battery is about 5 to 7 years. Similarly, most batteries are rated for 700 to 800 charge cycles before they lose 20% of their original capacity. Using our Omega, for example, you would have to ride about 48,000 MI to hit that many charge cycles.
So far, we have only seen a handful of customers pass the 20,000-mile mark, and all of those were 5 years or longer. To put that another way, even our customers who use their bikes the most would not see any benefit from this charging strategy.