Hello, Is there such a thing as a battery-based car battery charger? I've seen the 100CCA duracell units at BJ's for $50, which can be used as a jumpstarter... What Im looking for is something that will just trickle or charge (2A, 5A, whatever, obviously a cigarette lighter is current limited). Smart is better - only feed what is really necessary to the battery. Is there such a thing? Given that the duracell jumpstarter has a 12V DC lighter port, I would think that hooking a dual-male cable could allow the notionally higher voltage charger battery to charge the lower voltage starting battery. I would think that a diode would be necessary inline. Obviously a self-contained smart item would be preferable... Any thoughts? Thanks!