I've only had it for a couple days, but it works great so for. I tested it and lets the volts go through like I need to charge the other battery. When I turn the car on you hear a heavy click, witch I have to say I like to hear. For the price and the amp of the relay it's a good buy. I bought this one, because I want to upgrade the alternator on my car. I wish Sonic sold that too, but maybe some day.