Heck, in another thread we learn that Interstate golf cart batteries are warranted for only
6 months, so that makes Trojan look pretty good.
However, Concorde/Lifeline, an aircraft battery manufacturer and one of the best batteries around offers a 12 month replacement warranty and 4 additional years pro rated when used in RV and marine applications. Cost is 10-15% higher than a similar Trojan, though.
Optima Blue and Yellow deep cycles have a fairly generous 18/18 month warranty on the label but lists the exceptions below in a pair of footnotes. And Optimas cost quite a bit more than Trojans as well.
3. Deep cycle models, when used in series string applications with battery management system or CV/CC charge method have 12 month warranty.
4: Deep cycle models, when used in series string applications without battery management system or CV/CC charge method have 1 month warranty.
Optima warranty