no no no! There's no way to make salt an acid. Salt is the byproduct of a neutralized acid, the reaction does not go the other way. And ammonia does NOT neutralize acid either. In many cases it doesn't do anything but mix with acid and make a stinky acid. (You don't want it near bleach either or you'll get a poisonous gas)
The fired black powder residue should be mostly carbon with some sulfur compounds in it. The sulfur compounds are what can become acidic when mixed with water. Its basically the same as acid rain. That was caused by coal burning power plants that let the sulfurous smoke go up into the atmosphere. It mixed with the rain clouds and became a weak form of sulfuric acid.
Now that's totally different than the salts released/deposited by corrosive primers and what's going on with the car battery. 3 different reactions/situations.