You simply need to find a source of power from a circuit that’s only hot when the ignition system is “on,” and run it to the relay. The solenoid isolator is relatively inexpensive-it’ll set you back less than $20. Turn the ignition system off, the relay switch opens, preventing current to flow from either the chassis to the RV, or vice versa. When your vehicle is running, current throws the switch closed to allow current to flow from your vehicle charge system back to your RV. Somewhat comparable to a vehicle starter relay, the solenoid is a big electrically operated switch. The simplest battery isolator is nothing more than an electromechanical relay. It used to be there were just two kinds of isolators now there are three.

At the same time, the isolator allows your house batteries to charge up by drawing on your chassis or tow vehicle alternator. Without such isolation, your house battery and SLI battery will seek to maintain the same charge level-and if that’s too low to start your rig, you’re left in the lurch.

The RV had “stolen” power from the truck battery, leaving us wandering around with a set of jumper cables, looking for a hot jump.īattery isolators do just what it sounds like: They isolate your RV “house” batteries from your vehicle’s SLI (starting-lighting-ignition) battery. After our first night on the road, a chilly one where the furnace ran during the night, we found we couldn’t start the truck up. On one of our earliest RV adventures, we learned the hard way about the importance of a battery isolator system.

Battery isolator relay