The RV industry uses golf cart batteries with two 6 volts in series with Trojan T-145s kicking out 205 AH in a six hour period. They don't look like your grandpa's battery but they are made for non-starting loads but they weigh in at 71 pounds a piece. I use them in my RV where size and weight isn't a factor and they last twice as long as any marine battery. The Costco version costs about the same as the marine batteries.

http://lemley.net/electric/trojan.html