I just received a Deka 9AGM49 from Remy Battery for my 2004 3.0i. It was just under US$200 shipped. The original equipment battery is 7 years old, so it's definitely due for replacement.

After ordering, I did a little more reading about AGM batteries, and I have to admit I now have reservations about putting one into this car. My concern is that the e53 charging system will charge it too much, or not enough, and then I'll just be replacing the battery again in 2 years. Maybe I shouldn't worry so much. Are any of you folks actually using this battery?

Anyway, I'll report back soon on installation.