It's weird. The battery is only about 10 months old. At the time I was in need of one ASAP so I bought a Duralast Gold (900CCA, H8, Size 49, etc etc). I went for a test drive today and it looks like load voltage on the alternator was hovering between 12.7v - 13.1v. Resting with the car off is at between 12.4v - 12.6v at the battery. Using the Hidden Menu 9 (Yes, I know, inaccurate) I think the culprit was probably my alternator the entire time.

While my battery was charging I decided to change my lower intake boot due to some lean codes I was getting. While taking things apart I noticed the alternator air duct was completely disconnected from the alternator! We've had a lot of rain up here and I can't count how many little puddles I've probably drove through. I'm going to load test the alternator with it running soon and see what's going on. Those volts don't look right to me. I may have to scrap a used one from the junk yard soon.

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'06 X5 3.0i