Be sure to match your usage (deep cycle or starting) and your battery. Like Charles Culotta, I use sealed Group 31 Delco 900CCA batteries (2 of them) for high amp, short duration loads (starting, windlass and bow thruster) and 6 volt Lifeline AGMs (6 of them totaling 660 AH at 12 volts) for low amp, long duration, deep cycle loads (i.e., house bank loads, mostly refrigeration). Sealed and AGM makes sense for me because I cannot easily (I know, nothing on a boat is supposed to be easy) get to the tops of the batteries to check/add water. The charging requirements are essentially the same. Gary & Gail M/Y Evolution 36' Krogen Manatee Anchored in Apalachicola, Florida