Solar cells are made of extremely high purity silicon wafers, which are specially treated to form two very thin layers. When sunlight or light is irradiated onto the surface of the wafer, the light can be converted into photocurrent and Light voltage. Current from the high voltage of the solar battery to the low voltage of the watch battery to be charged. In order to prevent the solar cell into the watch the voltage is too high, the internal diode and resistor to act as a buffer in order to protect the watch battery and life. Note: regular inspection of course, is inevitable, the other to note that the replacement of the battery must use plastic or bamboo tweezers folder, the use of metal tweezers easily lead to short circuit.