Weird Panel on the Bottom of the Wii

I just took advantage of Nintendo's free Wiimote jacket deal. (Yeah, apparently that's still going on.) While looking for the serial number for the Wii, I noticed a small, inconspicuous, removable panel on the bottom below the eject button:



I'm not really sure what it's for, but the best I could get from various Google searches is that it holds some sort of button-cell battery for keeping the clock ticking when its unplugged. That would make sense; nearly every computer has one of these hidden in them somewhere.

I'm afraid to actually remove the panel to see what's inside. First of all, because it isn't my Wii. It's my brother's. ^_^ Second, because there's a small, small chance it would void the warranty...not likely, but not risking it. Third, because I don't have a Philip's head screwdriver small enough to get the screw out...

I'll bet this little mystery is solved by the manual. Of course, I don't know where the manual went, so that's no help. :P