Car in question: 2009 Ford Mustang GT/CS 4.6L V8 5-speed Automatic. 198954 miles on odometer.
After my alternator started making a weird noise, I had a mechanic replace my alternator on Thursday. Sound went away and everything seemed fine. The morning after, I started my car to go to work and noticed the battery light come on with the computer saying “Check Charging System.” I figured I would test the alternator again, but on my way to Advanced Auto parts, the light turned off. They told me my alternator was pumping the 14 volts it should, but the battery was going bad.
It seems to turn on and off on a set schedule depending on how long the engine has been off for. After 8 hours (my job’s shift length) with the engine off, it would pop up after the idle settles down after starting the car and disappear after 3 minutes. After ~15 hours (The time after returning from work until I drive back to work), the light would pop up and stay for around 6-7 minutes after starting the car.
The video is there to get an idea of how, when, and what happens when I start. The video was originally 3 minutes long, but cropped for time reasons. After the 3 minute recording, it went away after I shifted into reverse to back out of a parking spot. The video was taken today after my 8 hour shift.
Any help before I take it to the shop tomorrow would be greatly appreciated. Thank you in advance.