I just solved my red battery message problem. From my research, 4 things can cause that message usually. Bad main batt, bad aux batt, bad BCM, or bad alternator.


I checked both my batteries, both north of 12v disconnected. Alt was reading 13.8 or so at all times, so I concluded bad BCM. My local indy happened to have a used BCM that I swapped in, still the red message of death.


Replaced the alternator with rebuilt AC Delco (didn't feel like paying twice as much for rebuilt Bosch). Red msg has been gone now for 700 miles.


Moral of the story, even with alternator reading healthy on scangauge, you can have a bad alternator.


I've never had a more difficult time changing an alternator...drain coolant, remove radiator fan, remove two water hoses to get the alternator out the top. No room to get it out the bottom. very un-Mercedes-like.


David, in your case I'm guessing just the SBC battery is bad (assuming cranking is strong).

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Mark in MA
05 MB E320CDI 402k Granite Grey Metallic
05 MB E320CDI 267k Black
05 MB E320CDI 232k White
05 MB E320CDI 209k Tectite Grey
99 Dodge 2500 Cummins 5sp 148k
62 Jeep CJ-6 120k