I have had these on my powerboat since I purchased back in the "90s. I always get at least 4 years service and sometimes more. I think that is good for any battery in such a harsh environment. Tried other vendors, but come back to Diehard.
Battery backup sump pump
So far, so good, had a short in my older battery, put this one in, has been hooked up for 3 weeks and power check still shows full. Had refrigerator (gas) on also, turned lights on off, still shows full. Think i solved drain problem on my RV. Will see how long this one lasts.
My other battery died all of the sudden and Sears had this battery in stock. My car seems to drive better with this battery like there is more pep in the motor.
Had the original for a very very long time. Just replaced it after at least 20 years