couple days ago i tried to start my audi 2.8 quattro 99.5 and couldn't start i started with jump cables and works and next day in the morning same thing, i think its a battery but not sure. thanks

 

You're probably right.

 

My brother had the same thing happen to him in his 1.8TQ ..its a cable somwehre by the battery!
He would jump it and a sec later it would start then an hour would pass and it would die! but then when he hooks it up to jump it and turns it on it works right away!

he went and got it fixed. he said its some cable. they replaced his battery and the cable.

 

could be the cable, could be the alternator, could be a battery too (does the battery have enough fluid?)

 

either the battery or alternator. that happened to me, also check the wires connecting to the battery.

 

Easiest thing to do... Take it to advance auto or autozone or some place like that. they will check for free and tell you if its your alt, batery or your avacado.