I guess I am not completely accurate after thinking about it. It depends on where the batteries are at, how they are hooked together determining the resistance on the leads from battery to battery. Either way, hooking to each terminal on one battery will work just fine. To be 100% sure you are putting the same amount of charge into each battery which really isn't all that important, you will have to connect one lead to each battery, again depending on resistance determined by the lead length/material and connection integrity.