Optima Batteries
http://www.peachparts.com/shopforum/diesel-discussion/311902-optima-red-top-1985-300d.html
Apparently Optima's are not as good as they once were.
Also remember you Battery life also depends on how easy your Engine starts = Valves adjusted correctly, Glow Plug system working good, Fuel Injection Pump timing and Injectors within specs.