We have 10-6v golf cart batt's for our house bank with pretty hefty loads. 150 amp/hrs/day sitting at anchor
, 300 amp/hrs/day under way. Our Trojan T-125's lasted 5 yrs cruising 99% of the time, no marinas
and never letting the bank go below 50% discharge or 12v. Replaced them in Aus. for 10 Exide brand golf cart batt's for $2200au!! I used to pay $52 ea , for Exide's here in So Cal
as we are close to the manufacturer. Had 4 on a friends boat for 14 years!
If you call around, you can find good prices on 6 or more batteries.