In a 48 to 72 volt lead acid battery pack, all of the batteries are meant to work as a matched set —and once they’ve been used together, they don’t age the same way as a brand-new battery. 1. Series connection = weakest battery controls everything A 48-72 volt pack is usually four to six 12V batteries wired in series. The same current flows through all of them, so if one battery is weaker: It discharges faster It can get overworked It limits the performance of the whole pack