No battery, No electricity. The buit-in automatic mini device can generate electricity for illumination once water flows. The light will go out when the water is turned off. The illuminated color will be changed according to water temperature. 1.If the water temperature is under 25°C, the LED faucet light will emit green light. 2.If the water temperature is between 26°C 35°C, the LED faucet light will emit blue light. 3.If the water temperature is between 36°C 45°C, the LED faucet light will emit red light. 4.If the water temperature is above 45°C, the LED faucet light will flash with red and blue light, which warns you should be careful!. This product has water conservation and filter system in the connection to water tap, which are excellent in water saving.