I had one go bad within the 18 month full replacement period - got a new battery - no questions asked. It was my house battery. No issues with the other WM deep cycle / starting batt combo. Note: the final 18 months on the wtty is pro-rated. For full replacement, it is 18 months from original purchase date. My dockmates swear by Interstate, said the WM batts die about one month after the warranty expires.