This Solar Fountain pump can operate on solar light and battery power when set to the on position. In good sunny conditions the pump will be powered by solar energy. In addition the battery pack will be recharged by solar energy. On a cloudy day or night time the battery will automatically run the pump. If fully charged the batteries will power the pump for up to 4 hours. When the batteries gets depleted the system will automatically switch to be powered by the solar panel source and the pump will resume running when the sun come back out.