it was running and just quit. will not crank back without be

Took out the battery and carried it to Autozone. They tested battery and said that it was good. I put battery back in. Still wouldn't crank unless jumped off, and sometimes not even then. We jumped it off and carried car to autozone, they put it on the machine and said that it was a faulty alternator. Bought alternator and put it on, still wouldn't crank. Went back to them and they said of it must be the starter. It wasn't the starter. (at this time I took the alternator to another parts dealer and they checked the alternator 3 times and they said that it showed good every time.) Jumped it off and drove back again, they put it on the machine and said that it was probably the voltage regulator. Said that the voltage regulator was faulty and sending to much power to the battery causing it to over charge. It had a really strong smell of battery acid. He still says that it is not the battery ? After almost $500 we are now going to buy and a new battery and we will see.