So here's a stupid question. I found a neat little adapter that you plug into your 12v source, and it uses a 9v battery to maintain your settings like radio, etc. But I realized later that when the key is off there is no power from the 12v source. Does that mean plugging into it will also not provide juice to the electrical system unless the key were to remain on? I think I might have bought another paperweight I don't need.