[twindman]

I added 2 6 volt batteries the first year I had mine (previous Monty). Left the 12v and added a switch that will completely disconnect everything and pick which sets of batteries to use.
With that said, I leave my trailer for 8-9 months in storage with no problems. When I get it out, the batteries are still (mostly) charged. The complete disconnect is the key, I believe. I don't know if it matters that it sits in Arizona with temps ranging from 30-70 most of the winter. But as stated, I had both 12 and 6v batteries for 7 or 8 years before replacing them.