AFTER regular charging (to 100%) and your led is green, the charger is still delivering a minimal current, so the BMS can do its job. It will balance out the amount of Volts in every cell as good as possible, so they carry all the same/similar amount. This is a slow process, that is why it is advised to leave it hooked up to the charger for a additional 4~8 hours. It is not needed every charge cycle, but it is a bit depending of your use: daily commuter of weekend fun driver? In average you can say 1x every 5~8 charge cycles you have to do a “balance of cells”.
In the attached image you see:
– top: unbalanced; visually its even clear it is not optimal use of the capacity of every cell.
– middle: passive balancing (slowly fill all cells simultaneous the same and when one reaches its maximum stop charging all).
– bottom: active balancing: fill each cell to its max, compare and try to empty the highest a bit and use that energy to top up the lowest a bit. Trying to use optimal the already present energy in your battery-pack.
There is more going on in the background, but this is called balancing.
Short: leave your charger connected for 4~8 hours AFTER indication full (eg. a green light) once every 5 to 8 charge cycles. It will prolong your battery lifetime ; the most expensive & precious part of your ebike.
So by loving ❤ your batt 🔋a bit and maintain it, it will reward you in return with a longer lifetime.