One or more piezoelectric pads are disposed into a keyboard and electrically connecting to a rechargeable battery of an electronic device or a portable electronic device. When one button of the keyboard is pressed, the movement of the button pushes and deforms the corresponding piezoelectric pad to generate a piezoelectric voltage for charging the battery. The electronic device or the portable electronic device can deal with power shortage during usage with the feature of transforming mechanical power into electrical power by using piezoelectric pads in the keyboard.