I've ran 2 batteries for years I mean like 20+. A 1.5-2 amp charger will maintain them. But if you let the car set without a maintainer on it disconnect the batteries from each other. They will "tictoc". As mentioned they will never have the same charge. The lower one will suck of the higher one and become the higher one, then the same will happen again and again until they are both DEAD. I am currently using this charger and like it.