BMW 8 Series Stalling: Help Needed for High-Mileage Fix

I had nearly identical issues with my 2018 BMW 6 Series diesel last month. Battery was at critical levels, causing start-stop malfunction and unusual engine cuts. Diagnostic showed "Battery heavily discharged/defective" code. My mechanic explained that the original battery had degraded and couldn't hold proper charge anymore. Had to replace the battery with a new AGM type and get it coded to the car's system. Also needed alternator testing to ensure it wasn't causing the drain. This was quite serious since a failing battery in modern BMWs can mess with multiple systems. After replacement and coding, all issues disappeared, no more warning lights or engine cuts. Start-stop works perfectly now. Best to get it checked soon as these symptoms typically won't resolve on their own. Make sure whoever does the work can properly code the new battery to your car's computer.

Thanks for sharing your experience, this sounds exactly like what I'm dealing with! Everything matches up perfectly with my symptoms. Really glad you got it sorted. Do you remember roughly how much you ended up paying for the whole job? And has everything been running smoothly since the fix, or have you noticed any other issues pop up?

Hey there! Just wanted to follow up, yes, everything has been running perfectly since I got it fixed. The total came to 290 € for the battery replacement and coding work. Best money I've spent on the car honestly, the start-stop system is working like a charm now, and I haven't had a single engine cut out since. My mechanic did a thorough job testing everything to make sure the alternator wasn't the culprit. They explained that these modern BMWs are pretty sensitive when it comes to battery health, so it's worth getting the genuine parts and proper coding done. It's been about six weeks now and I'm really happy with how the car's running. No warning lights, no unusual shutdowns, and the start-stop is working exactly as it should. If you're experiencing the same issues, I'd definitely recommend getting it sorted sooner rather than later. It's a straightforward fix when you've got someone who knows what they're doing.

Finally took your advice and got my BMW checked out. Found a highly-rated specialist who diagnosed the exact same battery issue. They had the parts in stock and got it all sorted in a few hours. Cost me a bit more than yours, around 350 for everything including the coding, but totally worth it. Car's running like new now. The unusual engine cuts have completely stopped, and the start-stop system is working perfectly again. Such a relief not seeing those warning lights on the dash anymore! Really appreciate you sharing your experience, helped me avoid wasting time with trial and error fixes. The mechanic was really thorough and even showed me some maintenance tips to keep the battery healthy. Definitely keeping them as my go-to shop from now on. Just wanted to close the loop and let you know your advice was spot on. Thanks again for the help!