This is the Futaba SBS-01V Voltage Sensor.

FEATURES: Designed for use with Futaba Telemetry systems, this sensor indicates
            voltage of item to which it is attached
          Measures two types of voltage such as a main battery used to power a
            motor as well as receiver batteries
          One year limited warranty throuh Hobby Services beginning at date of
            purchase

INCLUDES: Futaba SBS-01V Voltage Sensor with Fuse and Heat Shrink Tube and
            Instructions

SPECS:    Range: EXT line voltage, 0.0 - 100.0V
                 Normal line voltage, 3.5 - 8.4V
          Total Length: 34.2" (870mm) including wires
          Weight: 0.211oz (6.0g)
          Voltage: DC3.7 - 7.4V

                                                                   jxs 04/18/13
                                                                         ir/jxs