Mercedes V Klasse auxiliary battery issues

The symptoms you describe do suggest a failing auxiliary battery. A voltage drop during engine start can certainly trigger a cascade of electrical issues in modern vehicles, especially those with sophisticated power management systems. Does the error message appear consistently, or is it intermittent? I experienced similar issues in my V Klasse. Have you load tested the auxiliary battery to confirm its condition?

The error is pretty consistent, showing up almost every time I start the car. Intermittent at first, but now it's more frequent. Load testing, you say? How would I go about doing that? Is it something I can do myself, or is it better left to a professional? Any advice on the best way to proceed? I'm trying to avoid unnecessary expenses, but I also don't want to cause further damage.

Given the consistency of the error message, a failing auxiliary battery is highly probable. While load testing can be performed with the appropriate equipment, it may be prudent to consult a qualified technician. A diagnostic check will confirm the battery's condition and identify any other potential issues contributing to the electrical malfunctions. This could prevent further complications. A workshop should be able to clarify the issue.

Thanks for the advice. I took it to the shop, and you were spot on. Turns out the auxiliary battery was indeed the culprit. Replaced it, and all the errors are gone. Engine starts like a champ now, and no more electrical gremlins. The bill came to around 290€, which is annoying, but at least it's fixed. Appreciate the help!