To start off we go back to when my car sat for weeks at a time after i finished my build.

If no one had started it for awhile the battery would be die. Qucik jump start and it would start right up hold perfect voltage. And as long as you drove it, it would always start after that.

Fast forward to where i drive the car more often. One day im down the interstate and my battery light comes on. Voltage is fine no other dash lights are on and everything operates as normal. The light would come on and off periodically but more off then on. about a week of that I finally go get it checked out because the light started to be on more than it was off. The test showed that the alternator had a faulty voltage regulator. so I go ahead and order an oem alternator.

before I got a chance to install the alternator, I drove the car around often. I would say its 50 50 as far as a light being on and off when I was driving it around. However whenever it was on performance was never affected. but slowly I started to see that when the battery light was on the heat wouldn't even turn on and then eventually the brake light warning beeped and showed off on the info screen. even though they still worked.

At this point the signs seem consistent with an alternator on its way out. So I finally got to switching out a bad alternator for the new one and thought it would be the end of it. I start it up and see that the voltage is reading perfect started up first time no problem but the battery light is still on. So I hurry over to get the alternator tested.

the alternator pass the test however now it was saying it's a bad battery. so I go and buy a premium battery install it there at the store and fire her up and still the battery light is on.

I asked them to come and test it out again, so they hook it up with the car off to test just the battery. 100% charge, working correctly.

Then he asks to to start it up to test the starter and alternator.

Starter passed

But when he tried the first time To test the alternator it saidvoltage too low for a reading.

He ran the test again and this time it went through and showed only a 56% charge.

I shut it off to test the battery again and sure enoufh it's holding power at 96%

At this point we went back to test my old battery to see if it definitly was a bad battery, and yes, that was a bad battery.

At this point in completely stumped. Im looking for my next move.

 

It's very common that a bad alternator can fry a battery and vice versa.

The battery light is usually only on if the battery isn't charging - meaning the alternator is not working. The light itself is triggered by a feedback wire on the alternator. I would check that all the wires are connected on the alternator and that especially that wire hasn't been damaged.
Next step is to confirm if the alternator is actually charging/turning on. can you confirm that if you rev the engine the alternator pushes voltage out and charges the battery?

Either step should point you in the right direction. I hope it is as easy as a wire that was not plugged in.