Abstract: The cathode of the water-activated battery is a chloride member with a silver coating on its surface or it is a silver-chloride cathode. The anode is a magnesium plate. The anode and cathode are spaced apart with a rigid spacer member. A battery casing encloses the electrodes. A conductive liquid such as saltwater enters the housing through entry and exit ports formed therein and the water then surrounds the electrodes. Lead wires, e.g. a wire bundle, project through the casing wall and they connect to a light or a similar load. The battery is operated by immersing the housing into the conductive liquid, removing the entry port plug from the entry port to permit the conductive liquid to enter the casing through the entry port, and removing the exit port plug from the exit port to permit the conductive liquid to exit the casing through the exit port.