I was driving approx. 70mph on the interstate when my Audi A4 started to decrease in acceleration. It bucked a few times down shifting into lower gears as I pulled over to the shoulder. Put it in park. Tried to restart it and engine wouldn't turn over. Had it towed. Driver suggested it was timing/serpentine belt. Is he accurate?
What happened when you tried to crank the engine? With a broken timing belt the engine would spin abnormally fast. With a charging system problem it would crank very slow or you'd just hear some clicking and any lights turned on would be dim. Without doing any testing it's impossible to say. I'd start by measuring the battery voltage to see if it is discharged.