Adrian,
Yep, the ISRI seats definitely rotate under the steering wheel if you collapse them forward. The battery flap on mine hinges and there is just about room to get the battery in and out with the seat rotated. Takes a bit of fiddling though!
I have had the seats out a few times, as I'm currently recovering them. If you look under the seat you can see a little folded metal catch on the left side (looking from the front of the seat). It's on the right in this photo, just to the right of the bar that goes accross the seat (this is part of the seat sliding mechanism). It's the sort of triangular shaped bit of folded black metal.
DSC02737 by
ClubJoker84, on Flickr
You need the lift the catch up with a long screwdriver or something while you slide the seat out. An extra pair of hands is helpful, but you can do it on your own!
Ben
