LiPo batteries are easily damaged by discharging below 3v per cell, but this is difficult to judge when in flight. This on board voltage monitor will warn the pilot of low battery state, and can be set to any voltage between 2.4 and 3.5 volts. Suitable for use with 2 to 10 cell packs. The number of Balancers you will need is the same as the number of cells in series (cells in parallel can share a balancer). So a 3s1p pack and a 3s4p pack would both need three balancers.