It's easy. All you need is a CR-2032 3V battery. Just unscrew the back, take out the battery (I use a flat bladed screwdriver to help me do that), put in a new battery, the Tamagotchi will beep and an egg will be on the screen. Press B and choose 'Download'. This will restore your Tamagotchi from when it went on battery with a cross through it. You may need to change the time.