Golf cart batteries
You will need two 6v Golf Cart Batteries, T-105''s or T-135''s. You wire them in series, plus to minus. You then have 12 volts. The reason to use them is that they are one of the few, and have no equal in price, that will take 1000 deep discharges and still function. "Marine Deep Cycle Batteries" are generally useless junk for a cruising boat. If you buy 4 of the golf carts, you will have a serious house bank. Sam''s Club has a good price on them, stay away from boatus/west/ripusoff stores, you''ll pay double for the batteries. The down side now is that anemic 35 amp alternator you most likely have will take forever and a month plus two days to bring back your house bank. You’ll need to upgrade the alternator to about 100Amp (max with a single pulley)and get a smart regulator. Two stage ok, three stage better. It’s a fun project and it will be worth it. Just don’t waste your money and effort on “Marine” batteries, they are for powerboat bozos.