This sensor enables you to monitor the battery pack while in flight via the A2 telemetry port of the RX. The Taranis TX alerts you when it is time to recharge the battery.
There are three voltage ranges to choose: 1S lipo for battery voltage range from 0V~6.6V, 3S lipo for 0V~13.2V and up to 5S lipo for 0V~19.8V. The sensor is set by defualt for 3S Li-Po. You will need a soldering iron to change this setting (solder jumper bridge on the PCB)