BMW MY08 X5 Battery Problem

[koolkat1973]

I replaced the original battery on my X5 back in 11/2014 and it was working fine until 2 months ago when things start to act up. I would go to start the car and it wouldn't start. So then I tried a couple of time afterward and it started. This happened 4 or 5 more times the past 2 months. So I've been doing alot of my own investigation. I've confirmed that there are no parasitic draw when in sleep mode (10mA after 30 minutes). I've confirmed the alternator is good as it's constantly putting out 13-14.5V at the battery as I'm driving or when car is started. I've taken the batttery to Advaced Auto Parts and they've told me that this battery is good based on their test.

So I attached a voltmeter on the battery last night and the reading was 12.5V. This morning, before I started the car I checked the battery and it was readying 12.3V which should still be good. Then I unlocked the car door with the key and after 30 seconds, the voltmeter would ready 9.2V. I was shocked to say the least. So I started her up and she started up and then alternator kicked in. When I turned her off this time, the voltmeter reading is back to 12.5V and it stayed that way. So I repeat the entire process of locking the door, waited, then unlocked the door and the same thing happend. Voltmeter reading went from 12.4V to 9.1V within 30 seconds to minute after unlocking the car. Is this a sympton of a bad battery? I'm clueless at this point what the issue would be and how a battery can go from 12.4V to 9.2V within a minute. Please help.

Thank you.

Kiet