A lead acid battery will discharge about 4% a week.
More info at the
Progressive Dynamics web site.
The PD web site was one of the first that came up for me on a Google search. The number they are using is inline with what I've heard from some sources, a little high compared to other sources (5% per month). A LiFePO4 battery will discharge much less when disconnected and may be another option.
My 150 watt solar panel on the roof does a great job of keeping the battery bank charge when the trailer is in storage.
