The Redarc SB12 Dual Battery Isolator uses a microprocessor-controlled solenoid to protect your car's starting battery from deep discharge while allowing your second deep cycle battery to power all non-essential loads including fridges, lights and all your other on-board 12V accessories. With a quality battery isolator like this Redarc unit, your car can simultaneously charge both the starter battery and second battery once the charge voltage is 13.2 volts or higher and splitting the two circuits automatically once you shut the engine off and the main battery reduces to 12.7 or lower. This keeps the starter battery full to fire your car back into life when its time to leave camp, yet still allows you to access the second battery circuit. By using a solenoid, this dual battery isolator or voltage sensitive relay is superior to equivalent diode battery isolators due to the voltage drop associated with cheaper and often less reliable diode-type battery isolation technology. This unit is rated for 100 amps with a maximum inrush of 400 amps. Which is great for most 4WD and off-road vehicles. Contact us if you have a 24Volt system or if you run Lithium Batteries as we also have Redarc options for you