To remove the 4-cell battery, flip the laptop over and remove the 8 screws from the base cover. Using a plastic scribe, pry the base cover from the recess points near the hinges. Identify and unplug the battery cable. Remove the 3 screws securing the battery, and lift it up and away from the system.
To reinstall the 4 cell battery, place it back in the system and tighten the 3 screws to secure it. Reconnect the battery cable. Place the base cover back on the system and secure it with the 8 screws.