I've got '07 BMW 328i, the car was built 11/2006. My stealer told me my battery is week, but can continue functioning as long as I use battery tender. I am in SoCal.
Currently it has the "white" oem battery with 90Ah and 720A (probably CCA). He said, they don't install "white" one's only "black". The "black" battery is an AGM, that's why.
Parts can sell me black for $269 - 10% if I want to install it.
Stealer says I have two options:
(1) buy the battery and he'll only install & register it for $148 + tax
(2) He'll supply the black battery and do the installation for $370 + tax for a total of $399.
There are 3 possible colors to display battery quality - Green for successfully charged, Black and then Yellow. Mine is Green, it's a nice visible green unlike some posters posted that kinda looked black with hint of green.