I just asked my local garage here who's familiar with BMWs about registering my battery and they can do it for $45, but they said the battery must be bought through a dealer. I can't recall exactly the reason he mentioned but it had to do with MY2008s and onward - their batteries use 4.8(something) and not 4.0(something). He said we can't and shouldn't go to Interstate directly for those.

Aside from the possibility that he's in bed with dealers (doubt it), could there be any truth to this? He has an E46 M3 and mentioned that he dealt with 4 battery replacements before realizing he couldn't get batteries from outside.

__________________
'08 X5 3.0si - Alpine White / Saddle Brown interior
Specs: Sport Pkg, Premium Pkg, Tech Pkg, Comfort Access, Aero Kit, Style 433 staggered 20s on Conti DWS
Mods: Carbon 35 tint, LED angel eyes, GP Thunder 7500k fogs, H&R 20mm/25mm spacers, clear reflectors, gunsmoke-tinted taillights
Coded: Digital speedo, windows/sunroof/tailgate close via keyfob

X5 pics at Flickr