This past year I replaced three Group 31 batteries on a Kenworth (Paccar) T-300 truck in our VFD that were OEM batteries from 2007. That's something like 15-16 years. We never had to jump it until the last month. It would get started maybe once every four to six weeks; it is on a 2000-gal structure fire tender.

The truck has no battery maintainer. Truck has a battery isolation switch to disconnect batteries, which I find is a real issue now with vehicles that don't get used regularly.