So I checked while cold this morning (car sat in garage in NC overnight, temp in garage probably ~45F). I had 12.24 V across the battery terminals before starting and 13.6V once running at idle after I backed it out so I didn't kill myself with the exhaust. So obviously the alternator is fine, just wondering is the 12.24V cold pre-start enough for the GP's. I read on the dieselgiant that I should have 12.5V and I know a dead battery often isn't too much below 12V. As an aside, my E320 had the same voltage cold pre-start and my F150 had 11.98 after sitting in the frigid cold without starting for 4 days and that batt is less than 6 months old.