After a disappointing experience with a Varta i1 - a couple of years ago in an emergency, I went with a LION AGM from ECP.
It was £134 with a voucher code and it is much better and takes deep discarges that the A8 does from time to time in it's stride.
This battery is £128 now with the HOLIDAY25 code.
http://www.eurocarparts.com/ecp/c/Au...65a45bd&000020
I used the coding 000915105CE which is for 95Ah AGM - not sure if earlier BEMs accept this code but mine (2006) did (got the code from a later model with stop start).
Only thing I might add is buy one locally so you can return it yourself if there is a problem, otherwise you risk having to post a 20KG battery which is classed as hazardous and costs about £60 unless you have an account with UPS or similar. Of course they will probably say no fault found and you will have to pay postage back to you or tell them to stuff it.