Well I have 'partially' sorted out my battery issue...
The guys @ Newcastle Auto Electrics have only just started stocking Bosch batteries, they were accidentally supplied the S3 (lower CCA and suited for early 90's cars with minimal electrics) by Bosch and since I was literally their first bosch customer they were unfamiliar with the product range.
They called Bosch and then had the S5 sent out and the guys swapped it over today for me when it arrived.
Bosch battery guide: http://www.bosch.com.au/content/lang...roch_Final.pdf
So it was $190 fitted with 3 years warranty, pretty good value imo!
So now I just have to get the new battery coded, hopefully by my friendly bmw dealer under the premium complimentary servicing package