Yesterday when i was driving my volt gauge went all the way to 18. So I stop the car open the hood and I heard a sizzling noise, then got hit in the face and a little in my eye with battery acid. I replaced the alternator and the car ran great and i went to get the bad alternator checked and it failed the test. So today I went to take the bad alternator back to the place where i bought it 2 weeks ago and it tests good now, I didnt beleive them so I took it to another place and it tested good. What could have caused this? Does it have something to do with the alternator doesnt work right when its hot?