Low Battery Light

I have a 2016 Chevy Impala LTZ. When I start it the low battery signal comes on. I am trying to figure out why.
It has a brand new battery
It was doing this same thing with the old battery
I just changed the battery on the key fab
The alternator has been checked and it is fine
The car was wrecked when I bought it on the front end. The engine was not damaged.
I had the car for a while after I bought it and this light never came on. I had it at a shop and when the guy came out with my key fab he started it with the fab. The low battery light started coming on after he started it like that. I had never used that method of starting it.
Since then I have had several people look at it and no one can seem to figure out what is causing it. Ordinarily, if I were going to keep it and drive it I wouldn’t worry about it. It has been doing this for about 3 years and it starts like a new one every time. But, I’m getting ready to sell it and it is not going to be a cheap car so, I don’t want this light to be coming on.

Any suggestions would be greatly appreciated..

Thks…

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