The Automatic 140 Amp Dual Battery Isolator is all you need to charge Two Battery Systems. Voltage Sensitive Relay cuts in at 13.3 volts and cuts out at 12.8 volts to ensure your primary battery is always charged and ready to start your vehicle. It's like having two separate power sources for each battery while only having one alternator! This isolator is safe for use even for your off-road needs in dusty, wet and unexpected extreme weather environments. Great for extreme vibration applications as well. This battery isolator suitable for 12V 140 Amp, Truck, SUV, RV, ATV, UTV, Boat and so on. Forget the traditional diode relays and so-called "solid state" devices that can rob you of almost 2 amps of output power! The Dual Battery Isolator is the unit designed with cutting edge programming to deliver best performance - with ZERO sacrifice. This compact battery isolator was built ultra-small to fit almost anywhere! A perfect fit under the hood to get close to your dual batteries. Cause your accessories to run from a separate battery while the engine is not working on your vehicle, and at the mean time holding your main battery charged and your vehicle always ready to work. Smart Charging:Automatically combines two batteries when charging and isolate two batteries when stop charging. IP67 Waterproof: It has better waterproof performance than other battery isolators on the market. Specification: Rating Voltage: 12V Continuous Current: 140A Cut-in Voltage: 13.3V Cut-out Voltage: 12.8V Waterproof: IP67 Battery Isolator Size:2.65 x 2.65 x 2inch Colour: Black Material: ABS Package Contents: 1 x 140 AMP Battery Isolator 1 x Blue Ring Terminal 4 x Screw