You'll need to order part no's (I got these from Listers Seat for around the £30 mark):
So all the info is in one place, my current battery is slightly higher CCA than the factory Varta that came with it:
(096 (278mm x 175mm x 190mm) same as recommend for an Audi S3).
Note that if you have some types of map (I have Revo), you will lose some settings. So I took my SPS and noted them down first so I could put them back on later.