Mercedes E Klasse Electrical Fault

Sounds like a real head-scratcher. I had a similar issue with my old BMW 3 Series, though the symptoms were slightly different. My ride would randomly throw error codes and the iDrive system would reboot itself every now and then. I also suspected the battery, but that wasn't it. It turned out to be a faulty ground connection somewhere in the chassis harness that was throwing everything off. Did you check the ground connections? Also, any aftermarket electronics installed?

Ground connections That's an angle I hadn't thoroughly explored. Where exactly should I be focusing my attention regarding the ground connections? And yes, there is an aftermarket dashcam installed, but it has been there for years without problems. Could that be the issue?

Regarding grounding points, I'd start by checking the main ones in the engine bay and the ones near the fuse box, especially if you've been poking around there. Look for corrosion or loose connections. As for the dashcam, even if it's been fine for years, it's worth disconnecting it temporarily to see if the problem vanishes. Electrical gremlins are sneaky like that. Honestly though, this sounds complex and potentially dangerous. It might be worth taking it to a reliable shop with experience in Mercedes electrical systems. Don't want to fry anything!

I appreciate the advice. As suspected, the dashcam was the root of the problem. Seems it developed an internal short and was intermittently draining the battery. I have since removed the dashcam and replaced the battery it was weakened beyond recovery from repeated deep discharge cycles for a total of 290€. The vehicle now starts without problems.