We are very conservative with battery use but often camp up to a week with no power. We use 2 6V golf cart batteries I bought at Sam's club. Bought them at the beginning of the 2009 camping season and they still seem to work just as good as new. I did install a 4 stage converter/charger in the trailer at the same time to make sure I had them fully charged and wasn't over charging them. What works for you will depend a LOT on how you use them and how often you are without power and how often you are willing to charge with a generator (if you have one).