Old Battery Acid on Carpet - Should I be concerned?

3.5 years ago, I stupidly had the car battery I exchanged sitting on the back of my seat, seats were down, hit the brakes hard, it spilled into the back of the seat and I didn’t notice until the next day, so damage was done. The dealer replaced the leather on the seat that was burnt up, the foam in the seat I believe, and supposedly the carpet on the back of the seat. they however did not replace the seat belt buckle which later left a stain on the clean leather, finally got the buckle replaced, then had the car detailed thinking the stain would come out, but no the leather started to peel up where that stain was. So now having an upholsterer re-cover that part of the seat with new leather, then we noticed there was a big stain along the back of the seat where the carpeted board is, and that carpet was coming unglued and the glue was corroded… it never ends! That stain had been there for a while, I don’t remember if it showed up after the dealer “fixed” the seat, or if it was there, but I thought that had replaced that carpeting. So the upholsterer is replacing the carpeted boards and the back of the seat too. But now, 3.5 years later I am putting a baking soda paste on every stained area I am still finding, the car has been detailed and I believe carpets all washed and cleaned, so my question is, at this point do you think I still have active battery acid in the car? in the carpet? At the time when it happened I didn’t put any baking soda on it, I didn’t know what I was doing, I just took it to get fixed.

There is a little movable flap/board with carpet that sits against the carpeted board on the back of the seat, the upholsterer is replacing the carpeted board that goes on the back of the seat, but not the flap/board, the flap/board has some little stained areas that probably/maybe are also from the acid. I just don’t know if its still a danger to me, if I touch any part of those stains, is it still active 3.5 years later, and after being detailed, this has driven me crazy for years. How do I know if its gone or not?

As long as the Acid has been neutralized then there shouldn’t be any more damage.

How do I know for sure if it is neutralized though?

I doubt it. Rinse it with water and that will reduce the concentration of acid that might remain. Blot the water up with paper towels. Liquid acid is just salt dissolved in water.