I did a few tests today.... The car has 0 battery drain when shut off. When off the battery reads around 12.5 volts. When I start the car it goes somewhere between 12.5 and 13 volts. It doesn't go above 13 volts. If I turn the headlights, fan or anything else, the volts drop to around 11-11.5 (that's with a high idle) I would think that the issue is the alternator.

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Current fleet-
1993 Mercedes 300SD
2004 Chevy Avalanche 4x4
2009 BMW 535i xDrive
1995 Saturn SL2
1993 Mercedes 300SE (parts car)

Previous Benz's-
2001 Mercedes SL500
1983 Mercedes 300SD
1980 Mercedes 300TD
1996 Mercedes E300D
1999 E300DT
1984 300TD-T
1988 Mercedes 560SEL (parts car)
1979 300SD
2003 E500
2004 S430 4Matic
2001 E55
2003 E430