The NXT rechargeable battery pack does not fit flush with the back of the NXT brick like the battery cover (used with 6xAAs) does. I don't have the battery pack (yet), so I was wondering how much depth it adds. I found a picture of the pack installed, which gives the impression that it may be a brick taller, or maybe only a stud taller. Exactly how much though?
It adds the same thickness as a studless beam indeed, or 8mm / 20 ldu.
(This is true for the grey 9VAC battery, but I suppose it holds for the white 10VDC one as well)