I typically run the engine for about an hour every 12 hours or so when racing and that seems to keep everything up just fine. My experience is that the autopilot uses over 1.0 A on average rather than the 700 mA advertised. Once when I couldn't get the engine to start, I got about 36 hours of autopilot usage out of the two batteries before they were too dead to run it. Of course other loads were there on a rationed basis: running lights, interior lights, windex light, radio, etc. Sort of a how long is a piece of string question.
