Captsin Sadler, Sorry, wish I had more memory than hair, but both are gone. I Anchored Joy off my shore home, had a solar charger, rarely stayed out over two days at a time, and would occasionally use a battery charger to shore power while beached. So, the answer on how long my battery would last is I haven't the foggiest! Check specs on newer autopilots, usually different battery drains for "holding course" and "correcting course," and a tender boat like an M15 changes her course every time you shift your gum to the other side of your mouth. I presently have two Group-27 Deep Cycles in Rejoyce!'s bilge to power her auxiliary, a 54 pound thrust trolling motor mounted just aft the keel. My third boat to go for electric auxiliary, I am obviously sold. But now I keep her in a marina with power at the slip, so recharging is no problem. My last one used solar chargers, 0.3 amp max charge rate, and I rarely had to drag the charger and long extension cord down to my private dock. John Butler, not a Captain, just a retired CG Commander. Do it now! You can't do it any younger…