Basically what Radio611 said, you can use it any way you see fit, if your vehicle sits on for weeks on end I highly recommend it, it can use any combination of the timer and voltage monitor you choose and can run relays/solenoids if needed for larger loads. If I didn't have my equipment all on the Retained Acc Power in my Silverado, I probably would have went the charge guard way to be sure my equipment turned off when needed, everytime you kill a battery that's 10% of its capacity gone. IMO well worth the money.