I am looking at building a custom powerbank with 3 or 4 cells in series to generate 11-15V. I am looking at some of the TI Li-Ion charger IC's BQ257x3 and BQ241xx. These are really nice IC's but don't charge or balance the cells individually. Of course, they do implement the proper Li-ion charge cycle with constant current first and then a constant voltage until the current drops. They also have over-voltage protection, temperature monitoring, and input current limitation, and that kind of stuff so do overlap in functionality with the battery pack protection boards that usually monitor individual cells.
So assuming there is a protection board on the pack that monitors at least the minimum/maximum voltage per cell and that the individual cells are all new and from the same brand/model and likely even the same production batch, would there still be a need to charge/balance all cells independently for the battery pack? Or can I just treat the 3S pack as a single battery and assume they all charge/discharge at the same rates?
The other question I have is if I use one of those charge IC's, which already monitor for over-voltage, (dis)charge current, and temperature on the battery pack, and turn off the output if the total battery pack voltage gets too low, is there still even a need for the protection board on the battery pack (as long as they are new and identical cells)? Or can I just hook up 3 cells in series directly to the charger without the risk of batteries over/undercharging and thus breaking or worse (provided the rest of the circuit matches safe charge currents at around 1/2C and voltage for those cells of course).