BMW i5 Battery Gremlins: Frustrated Owner Seeks Help

Had exactly the same issue with my 2021 BMW iX3 last month. The symptoms were identical, warning lights, start-stop malfunction, and weak starts. Turned out the auxiliary 12V battery was completely drained and wouldn't hold a charge anymore. The main issue was a faulty Battery Control Module that wasn't properly managing the charging cycles. The repair required replacing both the auxiliary battery and the control module. It was pretty serious since these electrical issues can cascade into other systems if left unchecked. EVs are quite sensitive to auxiliary battery problems because they run a lot of systems even when the car is "off." The technician mentioned these problems are somewhat common in BMW EVs after the 150,000 km mark. My advice would be to get it checked soon, driving with a failing auxiliary battery can damage other electrical components. Best to have it diagnosed at a shop that specializes in EV systems, as it's not your typical 12V battery issue.

Thanks for sharing your experience, that's super helpful! Sounds exactly like what I'm dealing with. I'll definitely get it checked out ASAP since I don't want to risk damaging other components. Just curious, do you remember roughly how much you ended up paying for the whole repair? Also, has everything been working smoothly since the fix, or have you noticed any other electrical quirks?

Hey there! Happy to give you an update on my iX3 situation. After getting it fixed, all those annoying electrical gremlins completely disappeared. The whole repair job, including parts and labor, came to 290 €, mainly for replacing the auxiliary battery and sorting out that Battery Control Module issue. I've put about 5,000 km on it since the repair, and everything's working perfectly now. The start-stop system is back to normal, no more warning lights popping up on the dash, and the starts are strong and consistent. Such a relief not having to worry about those unusual electrical glitches anymore! Honestly, it was worth every penny to get it properly diagnosed and fixed. It's running just like new now, you wouldn't even know there was ever a problem. Really glad I didn't wait any longer to get it sorted. If you're still having those issues, definitely get it checked out soon. These electrical problems can be a real pain if they're left too long.

Thanks for the detailed follow-up! I bit the bullet and took it to a mechanic yesterday. You were spot on, it was indeed the auxiliary battery and control module causing all the trouble. The mechanic showed me how the old battery was completely shot and wasn't holding charge at all. The repair bill came to around 300 for everything, which honestly wasn't as bad as I was expecting. Theyaged to fix it in one day, and I've got to say, the difference is like night and day! No more unusual warning lights, the start-stop is working perfectly, and those weak starts are history. Really glad I asked here first, helped me avoid weeks of stressing about what it could be. Car's running smoothly now, feels just like when I first got it. Sometimes it pays to just get these things sorted quickly rather than waiting for them to get worse. Thanks again for all your help!