Why is the BMS needed for a LFP battery pack consisting of many cells?
Answer: The Battery Management System (BMS) allows you to monitor the battery pack operation. Since the battery consists of a serial string of many cells, you need to monitor each cell to prevent from deep discharge or over charge. The BMS will give you information about the cell voltage levels and can issue warnings if there is a problem with any of the cells.
The BMS with balancing option will balance the cells (usually during charging) to make sure all cells have the same capacity (=voltage) levels.
The BMS also allows data logging so that you can see the history of the operation of the each cell in the battery. This way you can detect if there is any problem with one or more cells in the battery pack.