Jrelecs 2-in-1 1~8S Lipo Battery Low Voltage Buzzer Alarm for RC Helicopter - White + Black Use for 1-8S Lipo/Li-ion/LiMn/Li-Fe 1-8s RC Lipo Battery voltage Tester low voltage Buzzer Alarm Power volume display and low voltage alarm Supports reverse connection protection The factory default setting is 3.3V