[Skater]

Which battery, engine or coach?

If it's the engine battery, that's subject to the usual automotive drains. I let mine sit for weeks at a time with no problem at all. If yours isn't handling that it's probably time for a new one.

The coach battery is quite another story:

First, the converters in our B190s will kill them if you aren't careful about monitoring the fluid level and/or disconnecting them if you leave the camper plugged in all the time.

Second, the converter simply may not be charging it enough - they do go bad (mine is putting out 11 volts, for example - I plan to replace it before the season begins).

Third, even when my battery was good, it would drain over time when I had it in storage. I didn't have the time to figure out why, but Russell's idea is the way to do it.