You will have to remove the LCD Screen to get to two more small screws under the hinge attachments. Then two more screws to release the cover plate that the Touch Pad is mounted to (the entire remaining half of the main cover). Lift it up gently and the CMOS battery is located to the right of the Touch Pad position.
M53XX Series Disassembly Photos
http://dexplor.com/phpBB2/viewtopic.php?t=691
Look at the pictures, they have made it hard to access as it is hidden under a cover beside the CPU.