On cars I typically replace batteries at 3 years. Just "because". Though I have found on a couple Toyota products OEM battery lasting WAY beyond what I felt they should. Way back when I had a 99 Saturn SL2. When I got it the OEM Delco was still in it in 2008. I replaced it a year later only because working at night at O'Hare airport I did not want to be left out in the Employee lot at United with a "non-starter" LOL