Description:Unique DesignThis compact battery isolator features an ultra-small (2.6" x 2.6" x 2") design and can be installed almost anywhere! Designed for dual battery systems, fits most 12V/24V charging systems, auto-senses main battery the voltage levelApplicationVSR battery Isolatoris suitable for 12V 4WD, Truck, Marine,Caravan,Boat,SUV, RV, ATV, UTV etc.Heavy duty silicone seal with reinforced housing inside is certified for off-road, waterproof, shockproof, dustproof, and safe to use in any conditionSmart Battery Isolator This 12 volt 140 amp dual battery isolator cuts in at 13.3 volts and out at 12.8 volts to ensure your main battery is charged without worrying about getting stuck on the road with a dead batteryDesigned for dual battery systems.Suitable for most 12V charging systems.Automatically sensing voltage level of main battery. Specifications:Alternative:0-727-33Model:RelayFeatured Refinements:Split Charge RelayType:ElectricsColour:BlackMaterial: Plastic,MetalSize:6.8*6.8*5.3cm / 2.6inch*2.6inch*2.0inch HOW DOES IT WORK ?When the engine starts and the starting battery voltage is higher than the Gut-in voltage, the Smart Battery Isolator (SBI) remains engaged and both batteries (starting and house) are charged simultaneously. The unit indicator (LED) lights up.When the engine is stopped, the batteries are no longer charged from the alternator and the loads connected to the batteries begin to drain them. The unit indicator (LED) lights up.When the voltage is lower than the cut-off voltage for 5 seconds, SBI senses it and disconnects the two batteries. The device indicator light (LED) is off.When the vehicle is restarted, the starting battery has reached the cut in voltage and the SBI is engaged again. The device indicator (LED) lights up. Package Include:1 12V Split Type Charging RelayNote:1. Please allow 1-3cm (0.4-1.18") difference due to manual measurement and slight color variation for different display setting.2. Due to the light and screen difference, the item's color may be slightly different from the pictures. Please understand.