Battery using seawater and power generating method

A power generating method of generating power supply by: guiding seawater through a reaction tank (7) having negative electrodes made of magnesium or aluminium alloy and a positive electrode made of silver chloride, causing the negative electrodes (5) to produce the oxidizing reaction of Mg->Mg+2e and the positive electrode (6) to produce the reduction reaction of 2AgCl+2e->2Ag+2Cl. A method of manufacturing the AgCl electrode is also disclosed.