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 .