I Was going to replace my battery UNTIL I had seen threads regarding the radio locking and having the right radio codes? Does this apply to a 2005 a6, or just older models?

Thanks!
Mac

 

You will need the code, though in practice I've discovered that if you are quick the radio doesn't go into SAFE mode. If you're unsure, then attach a 12v supply to keep the radio, and other settings stored whilst you make the change. This is by far the best method, because then all your stored settings will be kept, without, it's possible you may need to realign a number of modules, eg, throttle body, aircon, seat memory, interior lighting mode etc

 

Keep reading of radio codes and safe mode issues is of non-sense this days unless one does something extraordinary!

These times are long gone - disconnecting the battery causes only the clock to get off.
The rest of components are protected by auxiliary batteries or capacitors and do not lose their configuration.