BMW M4's Electrical Chaos: Bad Battery or Bigger Issues?

Hey there! I had very similar issues with my 2020 M3 last month. Started with unusual error messages and weak starts, just like yours. I found out it was indeed the auxiliary battery failing, these symptoms are pretty typical. When I brought it to the garage, they ran diagnostics and confirmed the auxiliary battery wasn't holding charge properly. They also found that the charging system needed some attention. In my case, they had to replace both the auxiliary battery and a voltage regulator. It was a more serious fix than I expected, as these electrical issues can cascade into other systems if left unchecked. The whole thing took about half a day to sort out. Since getting it fixed, my car's been running perfectly, no more error messages, start-stop works normally, and starts are strong again. If you're seeing these symptoms, I'd definitely get it checked soon before it potentially leaves you stranded somewhere. These electrical issues don't typically resolve themselves and usually get worse over time.

Hey, thanks for sharing your experience! That's really helpful since it sounds exactly like what I'm dealing with. Quick question, do you remember roughly how much you ended up paying for the whole fix? And has everything stayed running smoothly since then, or have you noticed any other quirks pop up? Trying to get an idea of what I'm in for cost-wise and if I should expect any follow-up issues.

Hey again! Happy to update you. Since my last post, I can confirm everything has been running perfectly smooth with my M3. The fix was totally worth it, cost me 290€ for the whole job, which included the new auxiliary battery and fixing the charging system. I know it might sound a bit steep, but considering how crucial these electrical systems are, it's money well spent. Haven't had a single problem since the repair. No more error messages, start-stop works like a charm, and those worrying weak starts are completely gone. It's been such a relief not having to stress about whether the car will start properly each morning! The best part is that the mechanic really knew what they were doing, they diagnosed it quickly and fixed it right the first time. When you find a good technician who actually understands these complex electrical systems, it makes all the difference. I'd definitely recommend getting yours sorted soon. These issues don't fix themselves, and you really don't want to end up stranded somewhere. Plus, the peace of mind is worth every penny!

Thanks so much for the detailed follow-up! Just wanted to update you, I took your advice and got my M4 checked out yesterday. You were spot on about the auxiliary battery! Got it replaced along with some electrical system maintenance. The whole thing set me back about 350 bucks, but honestly, it feels like a bargain considering how much better the car's running now. Took it for a good drive this morning and what a difference! No more error messages lighting up my dash like a Christmas tree, and the start-stop system is working perfectly again. The starts are super strong now, feels like a completely different car. Really appreciate you sharing your experience, it gave me the push I needed to get it sorted before things got worse. Glad I found a decent mechanic too. They knew exactly what to look for and fixed everything in just a few hours. Definitely keeping their number for future reference! Thanks again for all your help with this!