Cells have variances in their capacity, and the BMS works to even that out. This happens at the end of the charge unless your BMS has active balancing (most do not). When you charge to 100% battery, that is actually about 95% if the battery is healthy. That 0%-95% range is where 99% of your battery's energy will come from. The top 5% is where you will see balancing activity, which is why you might have noticed it sometimes takes longer to charge that last 5%.
So you might be wondering: Earlier we said charging to 100% isn’t as healthy, but now we are saying you need to charge to 100% to balance - so what do I do if I want to to be as healthy as possible? You can navigate this by charging to 100% right before you plan to leave again. As an example: You get home from a ride with 20% left and you’re probably not going to ride again for a few days. You charge your board up to 80% and unplug it (if you are using a Variable Rapid Charger you can set the charge dial to 80%). A few days pass, and before leaving on your ride, you plug it in again to charge to full. Once you’re full you head out!