To remove the 3 cell battery, loosen the 8 screws securing the base cover. Pry the cover away from the recess points near the hinges to lift it off the system. Find and unplug the battery cable. Identify the battery and remove the screw securing it. Lift the battery out of the system.
To reinstall the 3 cell battery, place it back in the system and tighten the screw. Plug in the battery cable and secure the base cover with the 8 screws.