This cover keeps the RAM levers out of the way of the battery and secures the hard drive. If you got a little overzealous and broke yours, here's how to replace it.
Use a coin or spudger to rotate the battery-locking screw 90 degrees clockwise.
Lift the battery out of the computer.
Remove the three evenly-spaced Phillips screws from along the rear wall of the battery compartment.
Lift up on L-shaped memory cover, slide it to the right, and lift it out of the computer.