I just replaced all the boat batteries over the last 2 months.
All are 12vdc, I had wondered about using golf cart cg2 batteries, but nixed the idea. Costs a lot more, and if one goes out, then I dont have 12 vdc and nothing will work.
I now have a Commercial Farm group 31 CarQuest for starting both engines.
https://shop.advanceautoparts.com/p...battery-group-size-31-950-cca-31p30/2100010-P
I now have two group 27 Duracell Deep Cycle from Sam's Club. At $82 each seems worth it.
https://www.samsclub.com/sams/durac...sel:people-who-viewed-this-item-also-viewed:9
The gen has its own start battery. As long as the gen starts it is never a problem, can use as much electricity as anyone could want out there.
I have no need for a larger bank of batteries. No gen, then that's a different story for me.
One weekend, all was fine, go out to boat midweek and 2 batteries went out with shorted cells, they were from 2012, so 6 years old.
I noticed the problem when checking the volt gauges, one bank was trying to charge at 15.6 vdc. And some gassing could be heard, batteries were warm. And when I pulled them out, some acid had leaked.
With the new batteries back to 13.6vdc.
My old Raritan 3 bank charger tries to compensate with failing batteries by raising the charge volts on whatever bank is going out. I had also noticed last use of boat, the house bank had run down a lot sooner than usual, I dont always run the gen.