take a look on evay for 4S BMS boards with the current rating which you desire. They usually do under voltage, over voltage, over current monitoring and they us some FETs to handle the current load. The FETs get turned off if the limits of any one cell are exceeded. Read carefully to get the right limits for your chemistry, the little monitoring chips are made with a variety of presets with various limits, although some allow for custom setting. Some have balancing features but i'm not sure how much real use or value that would be in your situation.