You gain access to the bios battery by lifting the keyboard. First, undo the external memory cover ( 1 screw) on the bottom of the laptop. Then you will see 2 screws which hold the keyboard down - undo these. Turn the laptop right way up, open it up and move back the 4 small keyboard retaining latches (located at the top edge of the keyboard). The keyboard can now be carefully tilted up by its top edge to reveal the motherboard with the bios battery there in the middle.