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, Starter/Alternator Cable for 2003 Mercedes-Benz C 230 | Mercedes- Benz Parts
12v Car Digital Battery Alternator Tester For Mercedes Benz W212 C180 E63 C300 E250 C E Glk Glc Gle Amg X204 W205 W203 W204 - Battery Measurement Units - AliExpress