I have a used 5th wheel that has two 6 volt batteries that are connected in series to make 12 volts. The batteries are going south(won't hold a charge)so I'm thinking of buying two 12 volt batteries and connecting them in parallel. Is this a no, no or are two 12's going to be alright? Also, regular car batteries or should I go with deep cycle? Any help would be greatly appreciated! Thank you. Keith