Abstract: A lighting device has a bottle, a bottle cap and at least one water-activated battery The bottle cap is mounted on the bottle and includes a light module having a printed circuit board (PCB) and a light source. The light source is mounted to a top surface of the PCB. The at least one water-activated battery is mounted between the bottle cap and the bottle and includes a top end and a bottom end. The top end is connected to the PCB via contacts. The bottom end is disposed in the bottle. In use, the bottle is filled with water to make the water-activated battery soaked in the water. The constituents of the water-activated battery then chemically react to generate electricity to supply power to the light source. Therefore, the bottle can be reused.