In one aspect, a water-activated, ingestible battery, comprises a cathode comprising a metal oxide with a decreased amount of toxicity, relative to an amount of toxicity of other metal oxides; an anode comprising a biocompatible, water stable compound, the anode infused with benign cations; a separator between the cathode and the anode; a cathodic lead comprising a first conducting material, the cathodic lead in contact with the cathode; an anodic lead comprising a second conducting material, the anodic lead in contact with the anode; and a cell casing comprising a water-permeable biocompatible polymer, the cathodic lead, and the anodic lead, with the cell casing enclosing the cathode, the anode, and the separator.