Just fill this Water Clock with water and it never needs batteries. Eco-friendly clock is powered by water. After about a few weeks or so you just replace the water. Reduce your carbon footprint by keeping time with tap water. Time powered by water, another leap forward towards a greener planet. Feature - Color: Blue. - Material: Plastic+Electronic Component. - Size: 8.8 x 8.2 x 7.7cm. - Water clocks don't need batteries at all. As long as the bottle on the back of the clock is filled with water, the time can be clearly displayed, and it won't have to add water for weeks. - Electricity is generated by chemical reactions of water. The chemical reaction is mainly a common magnesium-aluminum metal element, does not contain any heavy metals and is to the environment. - Our product can work normally by adding clean water. When the product display is dim or disappear you need to add water or other liquids (except corrosive liquids) until the liquids are filled with positive and negative electrodes in the container. - You can add different kinds of perfume according to your personal preference.