Ava wrote:
It is a 12 volt system with more than one battery connected in series. That is positive cable to positive terminals and negatives to negative terminals assuming all are 12 volt batteries. Connected in series is still 12 volts but twice the amperage. Make sure all batteries are fully charged, at least 12.25 volts to a full charge at 12.75 volts.
Careful!!! This post has right and wrong in it. If you connect 12 batteries in series the voltage will add and fry your electronics. 12+12=24. What he described is hooking them in parallel with Pos to Pos and neg to neg. In that case the voltage will not add but remain the same as he described. So I believe that was a typo but if you were to find a diagram of batteries in series and followed it, you would be in trouble.