LOL....most modern vehicles cannot be powered by the alternator alone, probably not since the early 90's.
If the battery is weak, you have systems fail.
This exactly. My last truck had such a powerful audio system that I had to use a 2nd battery just for it. The dealer should have replaced it right there no questions asked, but they sound just like my dealer, Chris Myers GMC, terrible. I think it's time to call out these dealers who provide such (insert cuss word here) service.