I would start with checking the cable connections and then the batteries. If they are the original ones, they may need to be replaced. You can either buy a battery load tester or take them out to a local auto parts shop and have them tested. If one battery is bad, I would replace all of them at that same time. The bad battery will cause the good ones to go bad quickly. Before removing any of the battery cables, I would photograph each one and mark each battery cable as to position. A quick drawing with the battery connections (location and where each one goes) is a great tool when replacing them and getting the cables in the correct order. Don't try to do it from memory.
Paul
__________________
|