It can't hurt to have the battery removed when doing the removing/installing the seats but according to here at Renntech.org, it should be okay to do what you did:
http://www.renntech.org/forums/index.php?showtopic=5185&hl=seat++removal
I don't know how applicable the following GT3 instructions are but the author makes the point that you should be careful with the seat belt plug orientation else the "dreaded warning light."
http://gallery.rennlist.com/gallery/albuq41?page=1