Our truck has two batteries, the primary battery that starts the truck, and a secondary, deep cycle battery, that operates a hoist. I installed this so the two batteries operate their respective systems, but can both stay charged when the truck is running.The truck only gets used once every two to three weeks and I have to keep a trickle charger on this truck now, because it keeps draining the primary battery. The isolator keeps cycling on and off every few seconds and eventually drains the battSee full review