I'm building my BMS primarily to watch over the batteries. I have it on pretty good authority from a trusted collegue that there really isn't a lot of balancing involved for these cells. His advice was that the balancing was only needed about 1X or maybe 2X per year - for a daily driver.
The primary objective of the BMS is to watch the SOC of the cells and make sure no cells go above or below the voltage tolerance. In addition, it's good to make sure none of the cells overheat.
The BMS can help you ensure you don't overcharge a cell with a charger designed to handle the voltage of all the cells in series. Also, while you are driving, the BMS will ensure you don't kill a cell by overdischarging it. This can be pretty dynamic because higher current will also pull the cell's voltage down.
My BMS will have authority in charging, and will shut off the charger when a cell reaches a pre-set voltage. This (I hope) will reduce the risk of killing cells by overcharging or causing drama with an overheated battery pack.
I'm deciding what level of authority the BMS should have in discharging. It seems some level of limp-mode would be good at a pre-set voltage.
Anyway, that's just my take on the problem.
Good luck with your build!
