“I am using deep cycle RV lead-acid batteries.”
I get about five years out of mine the same. But I rotate them a couple times a year so that some do not get more primary input charging than others. If you leave them in one configuration the first couple batteries closest to the charge coming in cook more than the rest. So rotating them helps this issue and extends the lifespan.
Thank you!
I sure hope I get more out of mine than that, but that is about what I get in a vehicle. The batteries are easily the most expensive part of a system.