GT1 ,as You know OE fits great and are pretty reliable for the most part.I payed $210 on my 4.6is but the 06-4.8is has a 1 year old battery in her.
I tell you one thing about BMW,I found out about the bulletin on Valvetronic intermediate levers in the cylinder heads and I am not very happy having to be surprised every month with these cars.
Good luck with the battery

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2006 4.8IS
65K MILES
PURCHASED 7/13