V6-3.5L,I was just told that a tensioner or pulley could have caused my alternator to go bad and if not replaced could make the new one go

I was just told that a tensioner or pulley could have caused my alternator to go bad and if not replaced could make the new one go bad. My batter light came on this morning and I looked up what it might be. I went to autozone to have them check my alternator because my battery was not yet a year old and barring the fact that I might have gotten a dud battery I had them check my alternator. They guy said it was totally dead and that everything was running off the battery and that would drain soon. The closest place was the dealer. Later in the day they called and said my car would be ready