Depends on your usage. The first time the DW and I tried to boondock, it was in Yellowstone National Park in September. Translation - cold at night. We tried to use everything like we did with full hookups, and lost battery at 3am. It didn't last 1 night.
We figured that leaving the heat where it was warm in the coach kept the fan running so long that it ran the battery down. The next night, we put the heat down to 55 and threw quilts on the bed. When we got up the next morning, we turned up the heat and crawled back in the bed till it warmed up, then when leaving the coach for the day, turned it back down. The batteries lasted 2 nights, easily, and may have gone longer, but we ran the generator every other day just to be sure.
