I have 2001 x5 4.4 with 130k miles. On Sunday the battery light comes on when I was about 20 miles from home. I watched the voltage the rest of the way home and it slowly dropped from about 11.5 down to about 10.7 by the time I got home. I have a 6 month old battery and I charged it with no problem, but again the voltage dropped while driving. So, I ordered a new alternator. While waiting for the alternator to get here, I keep a trickle charger on the battery, so if I need to make a short trip with it, I can. I have taken it on a few short runs over the past few days, and watch the voltage. Yesterday I took it out to run a quick errand. On the 3 mile drive to the store, the batter light was on, showing about 11.4 volts. Then on the way back, the battery light magically goes off and voltage returned to 13.2. I've taken it out a couple times since, and it is just fine.

So, is this an alternator?? If so, how did it magically start working again, and how long can I plan on it working??