I tried this once. We put our TT in storage for 2 weeks while I had to return home. I thought the fridge would be find as I had enough propane. My wife went over to the storage lot after 3 days needing to get something from the TT. The food was already bad and smelling. She went back the next weekend to clean it out and turn it off. Yes, the battery was dead. I don't know how long it lasted, but it did not make it 3 days. I just had the standard battery that was put in from the dealer at that time (and only 1), so I imagine it was just a regular low end deep cycle. Don't do it unless you have more than 1 fully charged battery, or solar.