To remove an iPhone’s battery, turn off the iPhone, unscrew the two small screws located next to the dock connector, slide the rear panel towards the top section of the iPhone, and then pull it away from the iPhone. This procedure works for iPhone 4 and 4s.
Unscrew the screws attaching the battery connector to the logic board, and use a plastic opening tool to detach the battery connector from its connection ports. Place the end of the opening tool between the loudspeaker enclosure and the metal casing of the connector.
Insert one end of the plastic opening tool between the battery and the case, near the bottom edge of the iPhone. Run the plastic opening tool along the edge, and lift it up gently to separate the battery from the adhesive securing the battery.
Pull the exposed plastic pull tab upwards to lift the battery off the adhesive attaching it to the iPhone, and then remove the battery. If you are using an iPhone 5, repeat the same procedure, but use the plastic opening tool to disconnect the front camera, digitizer cable, LCD , and the sensor cable. Place a suction cup above the Home button, lift it up gently to open the case, and then remove the battery.