Mercedes SL Undervoltage Problem Solved

I had similar low voltage issues on my SL. Check the battery voltage when the car is off and again while starting. A significant voltage drop during startup points to a battery problem. Also, inspect the charging system output to ensure it's within spec. What's the battery health?

Thanks for the quick reply. What kind of voltage drop did you see when you experienced this? I've checked the charging system and it appears to be functioning normally, but I haven't load tested the battery yet.

The voltage drop was significant, down to about 9V during cranking. Given you've ruled out the charging system, a load test on the battery is the next logical step. If it fails, the battery is likely the culprit. I ended up replacing mine. Probably best to get it checked at a workshop.

Confirmed the battery was the issue. Had it load tested and it failed miserably. Replaced it, and the undervoltage issues are gone. Total repair was 290€. Thanks for pointing me in the right direction.