New Alternator - Battery Light Still Flickering
 

I found a lot of similar situations as this online but none of them had any posted resolutions. Documenting what happens for me in hopes of helping someone else in the future.

Just installed a new alternator and had a good two days of driving. Suddenly this afternoon just after starting the lights surged a bit and the battery light came back on. Checking the OBD the readout was back to the same as it was before the replacement.

Stats:

New Bosch Alternator installed 2 days ago.
OBD Readout: 10.6v - 11.9v
Multimeter @ Battery Engine Off: 12.28v
Multimeter @ Battery Engine Idle: 14v

Nobody around town is open for an AVR tonight. Hoping the alternator isn't already shot...

Update (11/28): After poking around with the multimeter a bit more started it up to test the battery at idle again. OBC was reading 13v steady! Took it for a drive and after around 2min it went back to the 11v range again.

Update 2 (11/29): I can't get in anywhere until Monday but the consensus of everyone I spoke to is that if the battery reads 14v at idle (regardless of amps) the alternator is not likely at fault and if the battery didn't lose charge overnight it likely isn't the battery either. Everyone thinks we're looking for a bad ground somewhere as others have alluded to in this thread. Guess I know what I'm doing this weekend. Will be taking it in Monday regardless to have everything load tested.

New alternator or rebuilt/recondition alternator? Since you recently replace it, it should still have a warranty (BMW parts warranty is 2 years with unlimited miles).

Did you happen to check your main fuses in the back in the truck area? the BIG 120 AMP ones? sounds like it might be bad, your OBC voltage is while running I assume? obviously not charging the rest of the system, measure the voltage at the battery while running next.

Alternator is from Bosch. Haven't even finished filling out the lifetime warranty registration yet. It's more about the work to get it re and re'd that's killing me.

Voltage at battery terminals while idling is 14v by my multimeter. Heading to check fuses now, thanks!

Ok if voltage is 14v at the battery terminals it will be a smaller fuse, something that deals with the ECU, most likely in the engine compartment in the ECU box.

Fuse seems like a logical possibility. If 14v is getting to the battery something is preventing it from getting through the car.

I can't begin to understand the complexities of modern auto electronics but if my main fuses are good (verified power dist fuses 200amp etc) then why does it have trouble starting and have lights dimming like a dead battery.

I haven't been able to get at my ecu box. The filter housing comes out no problem but the runner along the top (5 philips screws that just spin?) prevents me from opening it and its too dark to start prying at things.

The whole thing is very odd. I'm not thrilled on the idea of driving it but if 14v is getting to the battery I should at least be able to drive it somewhere to have it tested in the morning.

Update: After poking around with the multimeter a bit more started it up to test the battery at idle again. OBC was reading 13v steady! Took it for a drive and after around 2min it went back to the 11v range again.

Could be a loose connection somewhere? Or possibly heat related?

Could be a bad voltage regulator. The voltage regulator is located on the alternator.

check all connections at alternator , battery and in between including starter for possible green connections = corosion. (not making good connection).