Or you can unlock the OBC and check the voltage with the engine running.

Do you have a link for unlocking the OBC?

Have u checked connection with battery..is it strong? If u could check at home alternator..is it getting enough power while engine is working..

Have Autozone do the test, they may have to remove the battery and put a full charge on it to really test it. If you have a mutimeter check the voltage at the jumper terminals i the engine bay. Should read 14.5ish volts while running. Another easy way to check without a meter is to disconnect the negative battery cable at the battery while running. If the engine falters or stalls out, it's the alternator. This can be dangerous, so don't do it if you're not confident.

Just unlocked the OBC (really easy lol) to see what my battery voltage was while parked and off.

It read 11.3V.

I'm positive this is the original battery haha.

That's a little low, may have a bad cell or it's not being fully charged back up by the alternator. You need to check the voltage while running. I just went through all this a few month ago. Good luck

Thanks man, what did your car eventually need? I started my car and the battery light came on about 2 minutes later haha

well, mine was part of diagnosing an intermittent no start issue. My battery was also showing only about 11.5V after charging and testing at the local auto parts place. I did replace it because it was the original battery. I also tested the alternator at the parts place and with a multi meter at home. It showed about 14.5V under load, that's with the lights on and heater blowing, radio on, etc. So I never had a battery light on. It's been my experience with other cars that the battery light does indicate a bad alternator. But you really need to do some solid testing to make sure. Especially with these cars, the parts are expensive and the alternator is difficult to get at. The battery is the cheapest, easiest thing to replace but it may not solve your problem. Do more testing.

One last thing, an aftermarket battery is fine. But if you buy an alternator make sure it's BMW or the OEM manufacturer. Find the part on line BMW Parts Catalog then shop around.

11.3 is a little low???

11.9 v is 0% charge status!

11.3 is deader then dead.

Measuring State-of-charge - Battery University

Many BMW owners replace @ 50% (12.2v).