O2 came from the factory with Interstate Group 24s; they did well for three seasons and squeaked by for a fourth. My intent from the beginning when I ordered O2 was to use the factory batteries until their end of life and replace with Group 27s or Group 29s/31s After pricing Interstate, Deka, and others (all of which are good batteries) I ended up buying Wal Mart "Everstart Max" Group 29s (which I believe are made by Johnson Controls). The price was HALF of comparable other brands of Group 29s, so I figured if I got three years out of them, I was still several dollars ahead. I did a load bank test on them earlier this week; they passed with flying colors. Fourth season, here we come! Needless to say, they'll be load tested several times during the season, and if there's any sign of weakness, buh-bye! No, I never considered AGMs. IMHO they're too picky about charging voltages and rates. BTW O2 does have an onboard automatic charger - Guest 2610 or 2611; can't remember exactly which one. I actually had it on my 21'er before installing it on O2. To answer the previous poster's question, on O1 it was extremely nice to be able to plug in the charger and forget it vs. having to climb into the boat, pull the covers off the battery boxes and connect clamps each time....and then later have to switch them to the other battery....then later take them off and stow the charger. IIRC the automatic two-battery charger was only about $100.