Just thought I'd post to let everybody know that I did this job today in about 20 minutes and it was a piece of cake. The main problem is the retaining hex bolt which holds the battery in place, it's a bugger to get to, but with careful use of an alan key I unscrewed it and released the battery. Just a case of removing the trim above the battery and then deattaching negative first and positive second. Then reassemble in reverse order. It's a bit of a bitch getting the battery out on your own because of it's weight and position, so a second person is useful here. Strangely I didn't have to input any radio code when I attached the new battery. The ABS light was illuminated for the first few miles and that has now gone out and everything is fine. Better than paying Audi £183 for the job anyway.