BMW i3 Alarm System Dead? Check Your Backup Battery

Hey there! I've got some experience with hybrids (I'd say moderate expertise level). Had a similar issue with my 2016 BMW i8 last year. Love BMWs, also drove an X5 before. The symptoms you're describing sound exactly like what I faced. My alarm stopped working completely and showed similar fault codes. Turned out the auxiliary battery was totally dead due to age. Had my regular workshop replace it, cost me about 330 Euro all in. They also did a full system check to make sure nothing else was affected. Before I share more specifics, could you share: Are you getting any specific error messages? How long has this been happening? Has the car been sitting unused for long periods? This info would help me give you better guidance based on my experience.

Thanks for the detailed response! I have 141609 KM on the clock and just had my service last month. No specific error messages on the dash, but my mechanic pulled the codes and found alarm-related faults. This started about two weeks ago. The car gets regular use, driven pretty much daily. Interesting that you had a similar issue, makes me feel better knowing it might just be the auxiliary battery. Was the replacement pretty straightforward in your case? My warranty expired a while ago, so I'm hoping it won't be too complex of a fix.

Hey again! Thanks for the additional details about your i3. Since you mentioned regular use and recent service, this really reinforces my initial thoughts about the auxiliary battery being the culprit, just like what happened with my i8. In my case, the replacement was super straightforward. The workshop had it done in about an hour. They basically just had to access the battery compartment, swap out the old auxiliary battery, and reset the system. No complex rewiring or coding needed, thankfully! The fact that you're getting similar fault codes but no dash warnings is exactly what I experienced too. These auxiliary batteries tend to just quietly die of old age, mine was the original one from 2016, so it had a good run. Given your i3 is from 2014, I'd bet money yours is also the original battery. Cost-wise, even without warranty, it shouldn't break the bank. My total bill was around 330 Euro, but I've heard some got it done even cheaper. The part itself isn't too expensive, it's a pretty standard component. Want me to share the part number my workshop used? Might help you compare prices before you get it fixed.

Thanks so much for all this helpful info! That's really reassuring to hear about the straightforward replacement process and reasonable cost. Yes, please share the part number, that would be super helpful for getting quotes. You're probably right about mine being the original battery from 2014, so it's definitely due for replacement. I was worried it might be something more serious with the electrical system, but your experience has put my mind at ease. I'll get in touch with my workshop tomorrow and have them check the auxiliary battery first. Really appreciate you taking the time to share your experience in such detail. It's great to hear from someone who's already dealt with and solved the same issue!