This Solar World charger uses free solar power to bring new life to your Mercury and Ni-Cad (Nickel-Cadmium) button batteries. Simply put your button battery under the “clip”, and then attach the suction cup to a window that gets sun during most of the day. Most Zinc Air and Silver Oxide batteries can be replaced with a Mercury or Ni-Cad version of the same battery. Your batteries can be recharged 2 to 10 times or more. The manufacturer guarantees you a savings of at least 50% of the battery price when you use a Premium Mercury battery. The Solar Pocket Charger comes with detailed and informative instructions so you can get the most from your new charger. One year warranty.