Battery voltage sensor

Introduction:
  FrSky Battery Voltage Sensor is provided as Two Way Telemetry System’s Optional Accessory. There are three voltage ranges to choose: 1S lipo for battery voltage range from 0V~6.6V, up to 3S lipo for 0V~13.2V and up to 5S lipo for 0V~19.8V. Please check the battery voltage division ratio for each option below:

Recommended Voltage Option               Max Lipo Pack Count            Battery Voltage Division Ratio
           1S                                                                               1S                                             2:1

           2S                                                                              3S                                             4:1

            3S                                                                             5S                                             6:1

More detail：http://www.frsky-rc.com/download.asp