Yeah, what Hossfly said. You have to FORCE those little ma thingies into the battery. If the output of the forcer is not greater than the forcee, the forcee just kind of sits back and laughs at it. Automotive batteries are 12 volt (right), but if you don't have something that puts out at least 17 volts, you will never fully charge that puppy should it ever need charging. You gotta make that battery submit to your wishes.