i have a recently purchased a 1985 oday 31. the boat will be kept on a mooring. no wind or solar. i have a 2000 watt generator/inverter. i am replacing the batteries an am leaning toward wet cells based on Maine Sails' postings on the subject. i am wondering if there is any advantage...or disadvantage in replacing the group 27's with group 31's. thanks in advance for sharing your knowledge
Biggest drawback is size. If the grp 31's fit then you'll be fine with them. 31's usually don't cost a lot more then 27's. Don is right though that you need to know your loads and calculate them. If sailing off a mooring, with no solar, you'll only ever be using 30% of the banks total Ah capacity because you'll rarely if ever get them back above 80-85%. This is sometimes referred to as the "cruisers rule", cycling your bank between 50% an 80%. So a 200 Ah bank would give you about 60 usable Ah's if cycling between 50% and 80% SOC. If you added solar you'd have 100 Ah's your first day out because you'd be back at 100%, day 2 you'd have 60 Ah's before hitting a 50% DOD.
Bigger banks than you need and cycled less deeply will last longer but fit, space, weight and charging capability should also be a consideration..
Wet cells are fine AGM and GEL can work too but you do need proper charging equipment to deal with them.
