Bad Alternator?
 

Or is there something else that regulates the charging of the battery on 2004 X5 3.0i ?

Battery was replaced In December/January (Lead Acid H8)
worked fine several months then boom wouldn't start, dead battery. Took it to autozone, said battery was fine, alternator was shot.
About 1-1.5months ago replace the Alternator (Bosch 140amp reman)
And now battery dead won't start. Battery still tests good but by time I drive to autozone voltage drops too much to test the alternator.

At first I thought it might be the registration, but after doing some research on here, that apparently wouldn't cause it to go that quick and isn't needed for my model.

So for voltage readings at the battery today I did this.
It was was 12.2 when I woke up.
Started it, dropped to 11.4. Slowly worked its way up to 12.4. few mintutes go by still no higher than 12.4. Turned it off, dropped to 12.1.
Threw on the charger till 12.9, started it 12.2, idled 12.4-12.5. Took a 10-12 minute drive came home, left running at idle was a 12.1. turned off 12.2

So as I first was curious did I get a alternator that went after just 1-1.5months or What else in the charging system would prevent a full charge by the alt?
I don't think its a drain issue cause voltage has little to no drop if I don't have it on trickle charger.
(Yes I have also seen that usually I should replace with a AGM but wouldn't that just shorten the lifespan? but not by years lol)

It sounds like your battery is not getting charged but the problem could be a number of things. You should probably take it somewhere that can test the charging system properly. Not Autozone by the sounds of it.

Seems to bump up a couple volts while running, but then tops out before it should. So its almost like something is preventing it from getting a proper charge...
I suppose I could just say the Alternator is shot and return it under warranty before spending the bucks to have it diagnosed at a shop.
The voltage regulator maybe the culprit? if so isn't it attached to the alternator? If thats the case it would just be replaced with a replacement alternator....

Oh, and I've checked for codes with my scan tool (Launch CRP129) and comes up with zip zero nada

alternator.

- Check what you have in the car. Bosch and Valeo can be interchanged but best is to stick with what you have now.

- Stay away from local store alternator, it is all Chinese stuff.

- Bosch is AL0703N ("N" is new). About $200 online (FCPEuro, ebay etc.)

- Valeo is 12317551253, about $300 online or ebay etc.

If you want to be adventurous, then rebuild it with new bearings and VR, info on bimmerfest E39 forum.

The "new" Bosch alternator is made in China which why it is cheaper than the "rebuilt" by Bosch in Germany. That was the case for me anyway. Yes, the voltage regulator is part of the alternator. If you are not going have it checked properly a good guess would be bad alternator.

Check the voltage output when the car is running. If it is at least 13.7 volts, it's not your alternator. If it's not your alternator, it's probably parasitic drain. Something isn't going to sleep. The telematic unit is the most common culprit.

- The Bosch AL0703N I have in my garage right now (bought 2 years ago) is made in Mexico. Many people on bimmerfest E39 (5-series) use it without any issue, it is as good as factory.

- I am surprised the new Bosch is now made in China.

Another caveat is some theories out there is when the alternator fails, it kills that telematic unit. I suffered a alternator failure and soon after the parasitic drain coming from the common failed telematic unit occurred.

I went to the dealer for my 140 amp alternator. It was expensive but I replaced it nearly 10 years ago and have never had a problem since. :thumbup: