BMW i5 Alarm Dead: Auxiliary Battery May Be Culprit

Hey there! I actually faced a similar issue with my 2021 BMW iX3 last month. The auxiliary battery was completely drained, causing the alarm system to fail. It's a common problem with aging auxiliary batteries in EVs, as they power the alarm and other essential systems even when the main battery is disconnected. Had to get it checked at the service center. The diagnostic showed the auxiliary battery was well below optimal capacity. The technician explained that these batteries typically last 4-5 years, and mine was due for replacement. It wasn't a major repair, just a straightforward battery swap, but it needed to be done by someone who knows EVs well since it's connected to various electronic systems. After the replacement, the alarm system started working perfectly again. The whole thing took about an hour and a half. I'd suggest going to a certified EV specialist rather than a general mechanic, as they'll have the right diagnostic tools and knowledge for these specific issues. Hope this helps with your decision.

Hey, thanks for sharing your experience! Sounds exactly like what I'm dealing with. I've been looking around for a certified EV specialist, and your explanation about the auxiliary battery makes total sense. Would you mind sharing how much you paid for the battery replacement? Also, curious if you've had any other issues pop up since getting it fixed? Think I might take the plunge and get it sorted soon.

Hey again! Happy to help! Just to update you, I actually got my iX3 fixed last week and it's running perfectly now. The total bill came to 330 € for the battery replacement. Worth every penny though, as both the "Additional battery alarm system defective" warning and all related issues have completely disappeared. Since the repair, everything's been working like a charm, no more alarm system glitches or any other problems. The certified EV specialist I went to did a thorough job, and they even checked the connection to other systems while they were at it. The new auxiliary battery should last another 4-5 years, which gives me peace of mind. If you're on the fence about getting it fixed, I'd say go for it. These kinds of issues usually don't resolve themselves, and it's better to sort them out before they cause more problems. Plus, having a working alarm system is pretty important for obvious reasons! Let me know if you need any other info. Always happy to share my experience!

Thanks for all the detailed info! Actually went ahead and got it fixed yesterday. You were spot on about going to a certified EV specialist, what a difference compared to my last mechanic! They diagnosed it right away and replaced the auxiliary battery in about an hour. Cost me a bit more, 380 €, but they did a full system check too. The technician showed me how the old battery was completely shot and explained everything clearly. No more error codes or alarm issues now. The car feels much more reliable, and I've got my peace of mind back. Honestly wish I'd done this sooner instead of worrying about it. Really appreciate your help in making this decision. Definitely keeping this specialist's contact for future maintenance. Sometimes paying a bit more for proper expertise is totally worth it!