Features: Press the button each for time, you can complete the circuit connection and disconnection. The circuit switched on the red indicator, the voltmeter lights up at the same for time. The circuit disconnect red indicator light, the voltmeter goes out at the same for time. When the input voltage exceeds 13.3V, the circuit will be connected automatically. The voltmeter and red (LED) indicator will also be ON. When the input voltage drops to 12.7V, the circuit will be disconnected automatically. The voltmeter and red (LED) indicator will also be OFF. If two batteries are connected, then the voltage displayed on the voltmeter is the battery that has higher voltage. Only connect the battery that you would like test the voltage and disconnect the other battery.When the voltmeter is not working, press the button once, the voltmeter will display the value for 2 seconds. When the input voltage reaches lower than 11V or more than 17V, the circuit will be disconnected automatically to protect the main battery from over discharging or protect the secondary battery from high voltage impact. Designed for dual battery systems or second battery bank in your van, truck, RV, UTV, off-road vehicles, marine boats, etc. Enclosure offers complete for protection from dust, oil, and other non-corrosive material. Waterproof for protection up to water projected by a nozzle against enclosure from any direction. Specifications: Continuous current: 100-120A Instantaneous current: 160A Current consumption - charging: 250mA Current Consumption - Standby: 8mA With anti-reverse function Ambient temperature: -2050 Breakaway Delay: 5-10 seconds Recommended fuse: 80Amp Power stud: M6 copper screw nut Surge Protection: Built-in Note: 1.Please allow 1-2cm errors due to manual measurement, make sure that you do not mind before you order. 2.Due to the difference between different monitors, the picture may not reflect the actual color of the item. Thanks for your understandings. Package includes: 1x Voltage Sensitive Relay