Check your Battery Isolator
I was doing some off-season maintenance and ran across a very deteriorated battery isolator. It was the original Sure Power 1602. The terminals were fused together with rust and the top had big crack in it. Surprisingly it still worked but who knows for how much longer. If you have the original isolator it might be a good time to check it. Mine was located under the antifreeze overflow tank. It was pretty easy to replace.
2001 E-350 V10 EB50 Penthouse