What is the best method of charging 12V deep cycle marine batteries to prolong life?
I have been using a 15 amp on board charger and a 15 amp trickle charge I have used for years on several boats. Now I have run through 7 batteries in a 5 battery system in 4 years and the dealer says my charging set up is all wrong, despite what the boat manufacturer/ charger manufacture says. They ar Ameristart Batteries which don't seem to exist on goggle to ask them directly how to charge there product.

Thank you for your time!
Dr Eric D Swanson:confused:

Your batteries may be on continuous charging. You should maintain discharging of the same periodically say once in a week at least to 75% to be drained. (continuous charging without any drain is also harmful for batteries)