Two 6v batteries is the way to go. They are true deeeeeep cycle batteries and will take abuse such as discharging them to oblivion and bouncing back. Check out Trojan T 105's or T 135's. Check the height/width/depth of the batteries. Go to the Trojan web site for sizes. Height may be an issue. The group 31's will not be true deep cycle batteries no mater what the label says.
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