Bad Alternator?

[rhinod56]

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)