To remove the 3 cell battery, loosen the 8 screws on the base cover of the device. 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 4 screws securing the battery to remove it.
To reinstall the battery, place it back in the system and tighten the 4 screws. Reconnect the battery cable. Place the base cover back on the system and secure it with the 8 screws.