S4MAFIA

Hello everyone!
Beginning about last week or so, the car would have trouble starting from time to time. Eventually it would start. I figured time to do some tune up type stuff.
Two days ago I changed my spark plugs. After I got it all put back together, everything was fine. Car started good, no warning lights, nothing. Just fine. Now heres where it gets fun.
That night the red 'battery light' came on the right side instrument cluster. Car felt fine. Voltage read normal. Figured I'd check the battery anyways. Cleaned up the terminals and made sure they were connected good and the wires were legit. After that I took the battery to get tested. All checked out fine.
So the 'battery light' is still on and im stumped. Last night I was on the freeway and the voltage began to dance from 14-12. At one point it stayed at 12 for a while. And at another point it spiked to 16. The yellow 'battery light' in the middle screen came on and sounded an alert. The car went into limp mode. I was close to home so I got her there.
This morning I scan for codes, none. Car starts right up. Running normal again. Volts at 12 now. Red 'battery light' is still on. Hmmm. Interesting.
Now I have done hooours of research, and have come to no conclusion on what my car needs. I have confidence I did the spark plugs right, but could this be related to me changing them? Just a coincidence? Is the car not starting sometimes not related to this? My best guess is voltage regulator in the alternator is going out. But I really have no clue,
Any help would be greatly appreciated. Much love.

S4MAFIA