jlangham wrote:That's interesting because I've had about 4 of the errors in the past couple of weeks and now my car is completely dead in my garage! BMW is towing it to the dealer in about an hour and giving me a loaner. The service guy said it may take a while to diagnose. I told him that it seemed like the 12v battery based on info from this forum and my own testing, but this time plugging in the charger didn't correct it and then my alarm went off for about 30 minutes and then my car is dead!
I think your bad 12 V battery diagnosis is correct. I know that disconnecting the 12 V battery when the alarm is armed will set off the alarm, so if the voltage of your 12 V battery dropped low enough, I'm guessing that the alarm could be triggered.
If the 12 V battery is bad enough (e.g., an internal short-circuit), it would not hold a charge or its voltage would drop too low to boot the controllers necessary to enter drive readiness state. If (when?) that happens to our 12 V battery, I'll follow BMW's instructions on safely disconnecting the 12 V battery. Then, I'll charge it with a standard 12 V battery charger in hopes that I can charge it just enough to enter drive readiness state. If successful, I'll be able to drive to wherever I'm able to buy a replacement battery (hopefully, not the dealer).
A better solution might be to buy a replacement battery before the current battery fails. The shelf life of an AGM battery is very long because its self-discharge rate is very low.