Not sure about X5's but many modern alternators don't actually charge the battery until it falls below a certain voltage. Long story short, my father was having a similar problem with his Accord. I kept saying it was that PoS CD changer he bought off ebay but he insisted it was his alternator based on diagnosing with one of those cigarette lighter voltmeters. I replaced his alternator and had him read the insert that came with the rebuild. It fully explained that it will only charge when the battery actually needs it.


Tim