I renewed my battery to a BOSCH S4010 (UK110) from the bay, Car Battery World, and paid £78.95, with free delivery. Made for the job, and has ample power and CCA.
12V Bosch Car Battery 110 Audi A4 2.5,2.7,3.0 Diesels | eBay
Very happy with the battery, the speed of delivery, and everything else!!