Both of the other posts that responded to you have good information. You need replacement batteries that are made for the "house" portion of the RV, i.e., deep cycle. If they are going to replace them under warranty (I would be surprised if they did) okay.... If you have to do it with your own checkbook, definitely opt for AGM batteries. The issue of installing 6 volt instead depends on your space and checkbook available.
__________________
|