I don't know if there is a difference but in my 2006 Audi S4, it is located in the trunk.
In the trunk under the removable mat where the spare tire is located
Open your trunk, remove the carpet as if you are getting to the spare tire and the batterie is located there, remove it with a socket wrench and take it to your local autozone for charging.
The 2006 Audi TT has 20 valves.
The 2006 Audi A8 has a V8 engine.
The 2006 Audi A8 has 40 valves.
The 2006 Audi S4 has a V8 engine.
The 2006 Audi A4 has 16 valves.
The 2006 Audi A6 has 24 valves.
The 2006 Audi A6 has a V6 engine.
The 2006 Audi A3 has 16 valves.
The 2006 Audi S4 has 40 valves.