I got curious

[Emory39]

So... After reading a post that I can not locate at the moment. I go curiously; I unlocked the OBD and did the battery test as I was driving it fluctuate from 13.7-14.1 (great), but I notice that when I stop at a light or idle the engine the volts drop to 12.2 or whatever at the moment the battery w/o the alternator is. Is this something common? have you experience something like this? Do you think that the alternator is on the way out?

[srmmmm]

Not necessarily. If you're sitting at idle with the rear window defroster on and the seat warmers going, I'd expect your voltage to be under the low charging limit. As long as the voltage comes up to 13+ at 1200-1500 RPM, you're probably fine.

2002 X5 3.0 316,300 miles
2014 428i 24,800 miles

2004 325i sold at 123,600 miles
2001 325i sold at 66,000 miles

1970 Firebird - under restoration

[audiophool]

I can idle my BMWs with many electrical loads and still see 14+ volts. Plenty of parts places can load test the charging system, and most do it for free (hoping if there's anything wrong you'll buy parts there). Get it tested.

[StephenVA]

The actual test for charging systems is 1500 rpm with no system load from the vehicle. Then use a using a carbon pile heat sink to see actual Amp/volt output. You simply dial in total amp ratings for the alt and read voltage. It may take a second reading at 2500 rpm to see full alt output. Reading voltage only especially through the special tests will get you 50% insight, your missing what is the amp out put of the alternator.
The idle reading your getting is low for a at battery post reading with NO ACCESSORIES turn on. The Processed reading through the dash may be actual or an average it sees. Who knows?
When in doubt use a DVM test at the battery it self. Saves a lot of grief.

[Emory39]

I will do the volts reading on my 2001 3.0 X5 to see if there is a difference. Agreed that I'm not looking at the amps but every time that it drops to 12 the fan that was running at full speed dips for a second then goes back to normal