ZERO VOLTAGE DROP: Forget traditional diode relays and so-called "solid-state" devices that can rob you of nearly 2 amps of output power! The Dual Battery Isolator is the only unit designed with industry-leading programming to deliver performance - without any sacrifice. This compact battery isolator was built ultra- (2.6 inches x 2.6 inches x 2 inches) to fit almost anywhere! A perfect fit under the hood to get close to both of your batteries. VOLTAGE SENSITIVE RELAY: The 140 Amp Automatic Dual Battery Isolator is all you need to charge two battery systems. The voltage-sensitive relay cuts in at 13.3 volts and cuts out at 12.8 volts to ensure your main battery is always charged and ready to start your vehicle. Like having two separate power sources for each battery while only having one alternator! RUGGED DURABILITY: Unlike other isolators on the market, the 140A Dual Battery Automatic Isolator is IP65 certified. This international protection rating means your isolator is safe to use