BMW X6 Alarm System Dead, Fix Needed for High Mileage Car

I had a similar issue with my 2019 BMW X4 last month. The alarm system failed completely, and after diagnosis, it turned out the backup battery was completely discharged. My car wouldn't respond to the key fob either sometimes. The backup battery is separate from the main car battery and supplies power to the alarm system when the car is off. After 170-180k km, these batteries often need replacement. It's not a major repair, but it should be handled by someone who knows BMWs well since they need to reprogram the system after replacement. In my case, the mechanic also found that some connections were corroded, which made the problem worse. They cleaned the terminals, replaced the backup battery, and recoded the alarm system. The whole thing took about 2 hours. It's been working perfectly since then. I'd recommend finding a specialized BMW shop rather than a general mechanic for this kind of work. While it's not a serious issue that affects driving, it's important for security.

Thanks so much for sharing this! I'm actually facing the exact same problem with my X6 right now, and your explanation about the backup battery makes total sense. Definitely helpful to know about those corroded connections too, that's something I'll keep in mind. Just curious, do you remember roughly how much you ended up paying for the whole fix? Also, has everything stayed working properly since then, or have you noticed any other electrical quirks popping up?

Hey there! Yes, I remember the costs precisely, it was 330€ for the whole job, including the new backup battery, cleaning those corroded bits, and reprogramming the system. I'd say it was money well spent. Since getting it fixed, everything has been working like a charm! The "Additional battery alarm system defective" warning that used to pop up on my dash is completely gone now. The key fob works perfectly every time, and the alarm system kicks in reliably whenever I lock up the car. I haven't noticed any other electrical issues since the repair. Honestly, it was such a relief to get it sorted, you know how annoying these warning messages can be, especially in a BMW! If your situation is similar to what mine was, I'd say go for it. Just make sure you find a decent BMW specialist who knows what they're doing with these systems. Trust me, it's worth getting it done properly rather than trying to save a few bucks with a general mechanic who might not be familiar with BMW's quirks.

Just wanted to update after getting my X6 fixed! Finally bit the bullet and took it to a BMW specialist last week. what a difference compared to my last mechanic experience! They diagnosed it right away, turned out I needed a new backup battery too, plus they found some nasty corrosion just like you had. Bill came to about 350€, which wasn't too bad considering everything they did. They cleaned all the connections, put in the new battery, and reprogrammed the whole system. Only took them about two hours, just like you said. Been testing it for the past few days and everything's working perfectly now. Key fob responds every time, alarm kicks in properly, and those annoying warning messages are gone. Such a relief! Seriously appreciate your advice about going to a specialist, totally worth every penny to have it done right the first time. Thanks again for helping me avoid another mechanic nightmare. Going to stick with these guys for future BMW issues!