To remove the battery, loosen the 9 screws securing the base cover. Pry the cover away from the recess points near the hinges. Lift the cover up and away from the system. Identify and unplug the battery cable. Remove the 5 screws securing the battery and lift it out of the system. Flip the battery over and disconnect the cables.
To reinstall the battery, reconnect the cables. Flip the battery over and place it back in the system. Tighten the 5 screws to secure it and plug in the battery cable. Place the base cover on the system and secure it with the 9 screws.