The BERING Slim Solar Collection uses light as its energy! Because its energy source is environmentally friendly and infinitely available: Light! Not only sunlight, but any kind of light is converted into electrical energy by the solar cell under the dial and stored in a rechargeable secondary battery, a rechargeable battery. There is no need for frequent battery changes. The watch has a power reserve so that – once fully charged – it will run for 6 to 12 months, even if it is kept in complete darkness during this time.