A water activated battery characterized by a) At least one anode selected from the group consisting of magnesium, aluminum, zinc and alloys thereof; b) A cathode comprising at least one basic copper salt comprising Cu(OH) 2 combined with a copper salt CuX (with n-1 the molar ratio between the CuX and the Cu(OH) 2 in the basic copper salt), such that a discharge reaction in saline versus a Mg anodecould be written nMg + Cu(OH) 2.(n-1) CuX = Mg(OH) 2 + (n-1)MgX + nCu) on a skeletal frame, the cathode further comprising a soluble, ionically conductive material; c) at least one cavity separatingsaid cathode and said at least one anode; and d) a housing surrounding said at least one anode, cathode and cavity; (e) a lower aperture at the base of the housing for ingress of water and for expelling of heavier than water products of post immersion reaction, and (f) an upper aperture located near top of the housing for venting hydrogen generated by the post immersion reaction, wherein the upperaperture is positioned below the top of housing to create a cavity to provide a void for trapping hydrogen, so that hydrogen is only expelled from the cavity via the upper aperture after a quantity has accumulated, and is expelled in bubbles having a diameter of at least one millimeter.