I would also add that most cranking batteries are _not_ “deep cycle” batteries. If they go flat, the plates sulphate badly and damage occcurs even if you can re-charge them. This is more noticable on the merc optimax motors that do not like weak batteries at all, although in your case 4+ years is really good battery longevity anyway. My trollers hardly ever make it beyond 2 years, 3 at a max before I can really tell the difference out in current or wind. Cranking battery usually gets replaced with the trollers.2008 Pantera Classic2014 Mercury Pro XS 200