Lemon Rx 120A EC5 voltage and current sensor (5S LiPo or 21V max, 120A max.) for the telemetry system. The telemetry system must be re-calibrated for proper function. See user manual at the bottom of website for calibration instruction. Please note that operational voltage is (7.8V to 22V) or 2S to 5S LiPo can be used.