Battery turnbutton fell out. How do I remove battery?

I've got a PowerBook G4 whose battery release turnscrew just fell out along with two small metal rings (trim pieces for that ring it looks like). There's a plastic ring inside (broken). I don't see a way to release the battery from the bottom of the unit and, without doing that, I can't remove the two screws that permit me to swap out the bad hard drive. Any thoughts on how to remove the battery without a hack saw?