batteries and no easy way to increase the capacity. I ended up completely rebuilding the battery compartment to hold 2 4D house AGM's and one group 27 starting AGM. After three years of cruising I have found that 2 4D's is plenty. It might be nice to have more but I haven't needed it. I have 350 watts of solar and a wind generator so by around noon in the tropics I'm back fully charged. That's after a movie or two, anchor light, cabin lights and what ever. I run a generator about 45 minutes to heat water for showers and it's putting some amps back as well but generally speaking, I don't need it. IMHO, AGM's are the way to go. Out of sight, out of mind. They are sometimes a bit hard to find in third world countries and that's a pretty big down side but if you have good ones prior to departing, it's no big deal either.