Nowhere does it say that there is two batteries.

Yes, I do believe that BMW has two housings. Why not, a second housing is not all that expensive to make. Look at how much they charge for CA.

The door handles look the same but are different, do you really think BMW would make two door handles? The answer is yes.

The plugging it in is stated before the CA portion that says it has a replaceable battery. When the battery is low the car tells you and you need to replace the battery, not put it into the dash. The whole point of CA is so you don't put the key in the dash, hence the replaceable battery.