A4 decelerates and stops.

Sitting on the side of the road again. Bought this A4 Quattro last week in Texas. Drove home to LA and the car decelerates and stops. Noticed the battery light on and check the battery. It was almost 4 years old. Got towed to autozone and bought a battery. They checked the alternator and stated it was good. That was 6 days ago. Same thing happen today, got towed to Walmart and bought a battery drove roughly 20 miles and again it happen. Currently waiting on the tow driver who I am paying 250.00 to bring me the 71 miles to my house. Do any of you know if this is a problem in other A4s and could it be something other than the alternator? Thanks