Mine is a Generac just like Bruce's. It has a charging circuit to keep battery charged when it does it's weekly test run. I will go out and just fire it up and let it run for 30 minutes about once a month to make sure it stays charged.

Bruce, my installer explained to me that you can get an adapter for the flex line that will hook to a propane bottle. He said it will run good on propane but not have quite the power as NG. Be a real rare occasion to loose natural gas, but could happen in a bad flood given the right circumstances.