Remove the battery in your Nintendo 3DS to replace it with a new one.
Unscrew the four Phillips #00 screws along the top of the back cover.
Grab the top edge of the back cover with your opposite hand so that the cover does not fall back into place.
Pull the back cover up and away from the rest of the device to remove it.
Insert a plastic opening tool into the notch in the lower case above the battery.
Pry the battery up with the plastic opening tool.
Grab the top edge of the battery and lift it out of the lower case.