I wonder if I could jam two of these 6V battery packs (wired in series to make 12V) into the space of the PowerBook's battery, and get it to work?

http://cgi.ebay.com/2-RC-6V-NiMH-1400-mAh-Flat-BATTERY-FOR-RC-Car-Receivers_W0QQitemZ270341973720QQihZ017QQcategoryZ34056QQtcZphotoQQcmdZViewItemQQ_trksidZp1742.m153.l1262

If so, the cost would be only $26.

See why I am wondering what the function of the other contact pads is?