Alternator operating range?
 

Can anyone tell me what the operating range of the alternator, while running, is on a 2001 X5 4.4i? I am trying to figure out if the alternator is going or it is the battery. Thanks in advance.

Best way to test it is to have the battery charged, then do a load test with it running at 2000rpms to see if it is putting out the correct amount of amperage. Any auto-zone type place should be able to do it for free.

Just measuring the voltage at idle would only tel you if it isn't putting out anything, but wouldn't tell you the actual output amperage.

Thanks once again Weasel. This is what I did last night. With the vehicle not running, we put a load tester on, before applying the load the battery was in the green. We turned the load on and it quickly dropped to the yellow. Then we started the vehicle, and as you described at idle it showed 13 volts. Slightly revving the engine it we up to the green. Would you say I have a weak cell in my battery??

Todder