Use a Jump Starter (http://tinyurl.com/2wzah9) to boost your trolling motor batteries. I fished in a 6am to 4:30 pm tournament yesterday, and the wind was howling. Had to stay on the TM all day on high just to keep the boat positioned. Long about 3pm or so my TM was noticeably weaker. I knew it wouldn't last the extra 1.5 hrs.
Out came the trusty Jump Starter that I keep in the dry storage. I jumpered it parallel to one of the TM batteries and.. viola... it worked like a champ. We finished the tournament with power to spare. This particular one I have has a 12v port to run your night fishing lights, and has an extra emergency light built in, plus if you run down your starter battery this can jump start your big engine. I got mine at K-mart on sale for $24.99, and worth every penny.