Did my batery recently too. Must be the cold. Followed the Key Fob instructions and worked like a charm.

 

I changed the battery in my friend's 2006 A4 Avant Quattro tonight with a $100 replacement from O'Reilly that fit perfectly. I think it was an 8mm hex bolt for the hold down.

To avoid having to reprogram things, I simply connected my battery charger to the positive and negative battery cables before removing them from the battery. That way, the car never lost power.

After the new battery was installed, everything worked the way it did before.