I have a 1990 750il with a serious battery draw, and I've read around, I've heard that the cord that leaves the alternator trails next to the engine and can become corroded around 140k. I'm sorry but I missed your mileage, I'd say that should be the last thing you'd want to look at, though. It appears my 750 would need some serious work to get to that cord, as the alternator is midway down the front drivers side of that huge block.