I didn't have the battery tested, but I did check the voltage and connections.

Drove 200 plus miles yesterday with no issues. The battery light hasn't come on since. Odometer rolled over 288,888

I'm going to inspect the grounds and check the alternator connections.

 

So I haven't looked into this further yet. I haven't had a problem until this morning....
It was single digit temps last night. I went out to my car to go to work and battery light was on when I started it. Checked OBD voltage with my phone and it was sitting at about 8.8 or so.
Put a multimeter on the battery while the car was running and it was at about the same, maybe slightly more. Disconnected the battery from the car to take it to get a replacement (was new only 6 months ago) and checked the voltage it was about 10v. Came home from Napa with a fresh battery, tossed it in the car, started it up.
I get 8-9 volts on the OBD reader with car running.
Battery was 12.5v before I put it in the car, it is about 11 with the car running.

Something doesn't like the cold..... just not sure what yet.

 

Sounds like a dying alternator and/or dirty grounds.

 

But only when it's cold ?

 

This, given it's on when cold I'm leaning towards dying alternator

 

Well.... that would make sense seeing as I'm almost at 300k and never changed the alternator LOL

 

If you have a multimeter, you can run tests on it with the car running to help narrow down the problem to be sure.

 

Drove down the street a few miles. Voltage went back up to 14v from 11v, battery light off. Start it up back at home with no issue. Voltage 12v when off and then 14v when running. It was 17degrees out....
Going to try again in an hour when I have to go out for work. Supposed to be almost zero degrees tonight.... not sure if I'll take it to work and risk getting stuck. :-)
Going to swap out the alternator next week probably. Unless it dies completely, then I'll do it sooner

 

New alternator came from Rockauto at a good price. Tore out the old one today and opened the new alternator and the plastic cover was shattered.
I was unable to get the old cover off to switch over because all the bolts were too rusted, so I had to pick one up at Autozone.

Drove about 150 miles with no battery light on.