BMW 1 Series Alarm System Dead, Battery Backup Issue?

Hey there! I have some experience working on cars and had a very similar issue with my 2014 BMW 3 Series diesel last year. The symptoms were exactly the same as what you're describing with your 1 Series. Turned out my backup battery for the alarm system was completely dead. Took it to my regular workshop and they diagnosed it pretty quickly. Had to replace the entire backup battery unit which cost me around 330 Euro including labor. The car's been working perfectly since then. Before you proceed further, could you share more details about your car's mileage and whether you've noticed any other electrical issues? This would help determine if there might be other related problems we should look into. By the way, if you want to test this yourself, try disconnecting and reconnecting the main battery, if the alarm doesn't sound at all, it's almost certainly the backup battery.

Thanks for the detailed response! My car has 149297 KM on the clock and had its last service about 3 months ago. No other electrical issues that I've noticed, everything else works fine. I tried the battery disconnect test you mentioned and got no response from the alarm, so you're probably right about the backup battery being the culprit. Guess I'll have to bite the bullet and get it replaced. Good to know the fix worked well for you and wasn't too complicated. Really appreciate your help on this!

Hey again! Thanks for getting back with those details. Yeah, those mileage numbers and symptoms are really similar to what I experienced with my 3 Series. Mine was around 155,000 KM when the backup battery gave up. Since you've confirmed there's no alarm response during the battery test and you're not seeing any other electrical gremlins, I'm even more convinced it's the backup battery. The fact that your car had a recent service and everything else is working properly just reinforces this. Just want to mention, when my workshop did the replacement, they told me these backup batteries typically last about 8-10 years before failing. So timing-wise, it makes total sense for your 2012 model. Keep in mind that labor costs might vary between workshops, but the part itself should be pretty similar to what I paid. Let us know how it goes after you get it fixed. It's such a relief when these things get sorted out properly. My backup battery has been rock solid since the replacement.

Thanks so much for the additional info! Really helpful to know about the typical 8-10 year lifespan of these backup batteries, makes perfect sense why mine's failing now. I've actually just booked my car in at a workshop for next week. The quote they gave me was pretty close to what you paid, so that's reassuring. Funny how our cars had such similar issues at almost the same mileage. I'll definitely update you once it's fixed. Thanks again for all your help and for sharing your experience, it's made me feel much more confident about getting this sorted out!