BMW 5 Series Alarm Failure: Battery or Bigger Issue?

Had the exact same issue with my 2015 BMW 3 Series Hybrid last year. The backup battery was completely dead, and I experienced similar symptoms, no alarm response and error codes popping up. Got it checked at the garage, and they confirmed the backup battery had degraded due to age. It's a separate battery from the main one, specifically for the alarm system and some memory functions. The repair wasn't particularly complex, just needed a battery replacement and system reset. Not a serious issue at all, but definitely needs fixing to keep your security system working properly. The technician mentioned these batteries typically last 4-5 years, so the timing matches up with your car's age. Just make sure whoever works on it uses the proper diagnostic tools and genuine parts. Took about 2 hours total at the shop, including testing after installation. Worth getting it sorted soon to avoid any security risks.

Thanks for sharing your experience! Really helpful to hear it wasn't anything too major. My symptoms sound exactly like what you described. Can you remember roughly how much you paid for the whole job? Also, has everything been working fine since the repair, or have you noticed any other quirks with the alarm system?

Hey again! Glad I could help earlier. Just wanted to update you on what I paid and how things have been since. The total bill came to 330 € for the battery replacement and labor. Might seem a bit steep for a battery, but that included all the diagnostic work and system recalibration. They had to use genuine BMW parts, which always adds to the cost. And you'll be happy to hear that since getting it fixed, everything's been working perfectly! The "Additional battery alarm system defective" warning that was showing up completely disappeared after the repair. The alarm system now works exactly like it should, no more quirks or issues. Actually, it's been about a year since the repair now, and I haven't had a single problem with it. You know how BMWs can be picky about these things, but once you get them sorted with the right parts and proper installation, they're solid. Hope this helps with your decision. Let me know if you need any other info!

Thanks a bunch for all the details! Just got back from the mechanic today and wanted to share what happened. Turns out you were spot on, it was the backup battery. Found a reputable shop that specializes in European cars. They diagnosed it pretty quickly and confirmed the battery was completely dead. Paid about 350 € total, slightly more than what you mentioned, but they also found and fixed a loose connection in the system. The whole thing took about two and a half hours. They did a full test afterwards, and now the alarm's working perfectly. Even got that annoying error message cleared from the dashboard. Such a relief to have it sorted! Really appreciate your help in figuring this out. Saved me from stressing too much about it. Will definitely keep an eye on it, but feeling good about the repair. Thanks again for pointing me in the right direction!

I have an alarm with siren on a 530 eA hybrid with 66000kms that goes off randomly. The diag might be a problem with the alarm generator, which no longer correctly assesses the vehicle's inclination. I park most of the time on flat ground, I avoid ruts, I recharge the battery at home, the tires are inflated OK, the windows are closed OK, so it's an electronic problem. What is the price to replace this part? Thanks, CC

(Translated from French)

Before replacing the alarm generator, try recalibrating the tilt sensor first, as this might resolve the issue without needing a replacement. If recalibration doesn't help, consult a mechanic for a precise diagnosis and cost estimate. Let me know how it goes or if you have more questions!