I've been getting this message when I turn the AC (occasionally), when I don't turn on the AC it doesn't appear. Checked the the alternator voltage and its fine. Could it be
Battery alternator Visit Workshop — Mercedes-Benz C-class (W203), 1,8 л, 2005 года | визит на сервис | DRIVE2
Mercedes Benz battery alternator warning. alternator malfunction reset. 203 C class red screen - YouTube
Mercedes Battery & Alternator Check Via Secret Menu (Easy + Fast) - YouTube