a water - activated , ingestible battery consistent with this disclosure may include primarily biocompatible or non - toxic materials that are processed into a form factor , e . g ., a cylindrical form factor with a width of 3 mm and a height of 10 mm , that can be swallowed by an organism such as a human or other animal . the form factor may be an enlarged form factor when used for veterinary applications in large animals such as cows or horses . the potential toxicity of the battery is negligible . due to cost - effective materials and concurrent advances in clean - tech manufacturing , the cost of producing such a battery is low compared to the cost of producing a traditional implantable battery . orally ingestible batteries have a broad range of potential applications . examples of such applications can include powering edible gastric stimulators , edible biosensors , controlled release devices , and optoelectronic devices for optical sensing , gastric illumination , or photothermal ablation of tumors . the battery can be used to power medical devices that can also be swallowed . the battery may be directly integrated with the medical devices , or may be used to power the medical devices remotely or by tethered connection . examples of medical devices that can be powered by the battery include biosensors and sources of light , heat , or electric current . the battery can be used to trigger the controlled release of therapeutics , including small molecules and macromolecular biomolecules such as proteins , polysaccharides , dna , and rna , into the organism . a water - activated , ingestible battery may be used to avoid chronic implantation risks associated with traditional implantable batteries , such as infection , chronic fibrosis , internal tissue or organ damage , and leakage of battery contents . the battery may or may not be active or operational prior to ingestion by the organism . in the situation where the battery is inactive prior to ingestion , the battery becomes active after ingestion and integration into the gastrointestinal ( gi ) tract of the organism . the battery may be designed to activate at a predetermined time through the controlled presentation of an aqueous electrolyte . for example , the battery can be activated from the natural moisture of hydrated tissues in the gi tract of the organism or from an external source of water such as a bolus of water consumed by the organism . the battery can be integrated within the gi tract for a finite amount of time after which the materials of the battery can be either absorbed by the organism and eventually metabolized or excreted . in this context , active refers to the act of being functional as in the case of having an electronic load applied to the positive and negative leads of the battery . inactive refers to not discharging the energy stored in the battery . fig1 shows an example of a water - activated , ingestible battery 100 . the battery 100 may exhibit a form factor similar to that of a common pill . the battery 100 includes non - toxic materials that can be absorbed , metabolized , or excreted by an organism , e . g ., a human or other animal , that ingests the battery 100 . the battery 100 may include an outer casing 102 , a cathodic lead 104 , an anodic lead 106 , a water - permeable biocompatible polymer 108 , an anode 110 , a cathode 112 , a separator 114 , and cations 116 . the cathodic lead 104 , the anodic lead 106 , the anode 110 , the cathode 112 , and the separator 114 may be arranged in a planar configuration to optimize power output . the outer casing 102 of the battery 100 may include , for example , gelatin in a capsule form similar to those commonly used in existing oral pill formulations . the outer casing 102 encloses the battery components , such as the cathodic lead 104 , the anodic lead 106 , the water - permeable biocompatible polymer 108 , the anode 110 , the cathode 112 , the separator 114 , and the cations 116 . the outer casing 102 may protect the battery components as the battery 100 passes through a stomach and into a small intestine of an organism to ensure that the battery 100 is not subjected to caustic environments . the material of the outer casing 102 can be engineered to dissolve within a precisely defined time line . after dissolution , the outer casing 102 can be absorbed and metabolized by the organism , or excreted by the organism with other non - absorbed battery components . the cathode 112 may include a metal oxide with a decreased amount of toxicity , relative to an amount of toxicity of other metal oxides . for example , the cathode 112 may include a non - toxic metal oxide such as manganese oxide ( mno 2 ). in such an implementation , a phase of the manganese oxide may be a lambda mno 2 . other morphologies of manganese oxide may be included in the cathode 112 , such as alpha mno 2 and electrolytic manganese dioxide . the anode 110 may include a biocompatible , water stable compound . for example , the anode 110 may include a porous activated carbon electrode , an intercalated sodium titanium phosphate material , or both . an anode 110 that includes an intercalated sodium titanium phosphate material may offer increased performance with the addition of small amounts of benign metals such as titanium . the anode 110 is infused with functional , benign cations 116 . the cations 116 may include , for example , sodium , potassium , other benign cationic species that are naturally occurring in an organism , or a combination . the cations 116 may be loaded via chemical or electrochemical means into the anode 110 . the cations 116 serve as counter - ions during operation of the battery 100 . the separator 114 between the anode 110 and the cathode 112 may include a fibrous cellulosic material . the cellulosic material may be pressed into a thin film . the separator 114 serves as a physical barrier between the anode 110 and the cathode 112 . the battery 100 includes leads , e . g ., the cathodic lead 104 and the anodic lead 106 , that conduct electrons from the reaction areas in the electrodes to an external circuit . the cathodic lead 104 is in contact with the cathode 112 . the anodic lead 106 is in contact with the anode 110 . the cathodic lead 104 may include a thin film of conducting material , such as a gold material , a graphite material , a carbon material , a conducting polymer , or a combination . similarly , the anodic lead 106 may include a thin film of conducting material , such as a gold material , a graphite material , a carbon material , a conducting polymer , or a combination . the water - permeable biocompatible polymer 108 , along with the cathodic lead 104 and the anodic lead 106 , form a cell casing that encloses the anode 110 , the cathode 112 , and the separator 114 . the polymer 108 may include a polyester , an alpha - hydroxy polyester , a poly ( l - lactide ), a poly ( glycolide ), a poly ( l - lactide ) copolymer , a poly ( glycolide ) copolymer , a poly ( ε - caprolactone ) ( pcl ), a polycarbonate , a polyorthoester , a polyanhydride , a polyphosphoester , a polyamide , or a combination . fig2 shows a water - activated , ingestible battery , e . g ., the battery 100 of fig1 , during different stages ( a )-( d ) of operation . fig2 will be described in conjunction with fig3 , which shows a progression of the battery 100 through a gastrointestinal ( gi ) tract 300 of an organism during the different stages ( a )-( d ) of operation . the battery 100 can be selectively activated anywhere within the gi tract 300 through careful selection of materials and design of a geometry of the battery 100 . in stage ( a ), the components of the battery 100 are enclosed in and protected by the outer casing 102 , and the battery 100 is inactive . the battery 100 may be in stage ( a ) while the battery 100 is passing through a stomach 302 and into a small intestine 304 of the organism . the outer casing 102 can be engineered to dissolve within a precisely defined time line . the battery 100 progresses to stage ( b ) after the battery 100 passes through the stomach 302 and into the small intestine 304 of the organism . the outer casing 102 may have completely dissolved after passing through the stomach 302 . after dissolution of the outer casing 102 , the components of the battery 100 are exposed to an aqueous environment within the small intestine 304 of the organism . the aqueous environment may include an electrolyte 220 that diffuses into the anode 110 and the cathode 112 of the battery 100 . the electrolyte 220 may include sodium sulfate ( na 2 so 4 ). in some implementations , the electrolyte 220 is supplied through exogenous dosing such as consuming an aqueous solution of the electrolyte 220 by the organism . for example , the electrolyte 220 may be supplied by swallowing a 0 . 5 molarity ( m ) aqueous solution of sodium sulfate in coordination with ingestion of the battery 100 . the bolus of electrolyte 220 in the external environment will lead to diffusion of the electrolyte 220 across the polymer 108 of the outer casing and into the anode 110 and the cathode 112 to initiate battery operation . in some implementations , the electrolyte 220 may be loaded or embedded into reservoirs 222 within the polymer 108 of the outer casing . the electrolyte 220 may be solid electrolyte that dissolves when the battery 100 is hydrated by an external environment . hydrating the battery 100 in a natural aqueous environment within the organism will lead to diffusion of the electrolyte 220 and transportation of the ions from the reservoirs 222 into the anode 110 and the cathode 112 to initiate battery operation . the battery 100 can be activated by controlling the rate of hydration from the external environment . in some implementations , the battery 100 , without the outer casing 102 , can be immersed in water , the electrolyte 220 , or a combination of both prior to ingestion by the organism to activate the battery 100 . a time scale for water diffusion through the polymer 108 may be governed by engineering extrinsic factors , such as polymer thickness , and intrinsic compositions , such as polymer hydrophobicity , porosity , and tortuosity . controlling the time scale for water diffusion through the polymer 108 may be important for controlling a delay time after oral ingestion before battery activation . slower water diffusion can be used to achieve increased delay times so that the battery 100 becomes activated at a point that is farther downstream in the gi tract 300 , whereas accelerated water diffusion can be used to activate the battery 100 more rapidly . the electrolyte 220 permeates the polymer 108 and leads to activation of the anode 110 and the cathode 112 of the battery 100 to commence battery operation . at stage ( c ), the battery 100 delivers a current 224 across a hypothetical resistive load between the leads 104 and 106 . current is delivered across electrode leads 104 and 106 by migrating cations 116 infused in the anode 110 from the anode 110 to the cathode 112 . the current 224 delivered by the battery 100 may be , for example , approximately 0 . 1 milliamps ( ma ) at voltages less than or equal to 1 volt ( v ). the operation lifetime of the battery 100 may be , for example , approximately 1 hour for a total charge capacity of approximately 0 . 1 ma - h . after all energy has been dissipated from the battery 100 , the battery 100 , including the cathodic lead 104 , the anodic lead 106 , the water - permeable biocompatible polymer 108 , the anode 110 , the cathode 112 , and the separator 114 , may degrade , or break down , and may lose mechanical integrity at stage ( d ) as it progresses toward the end of the large intestine 306 of the gi tract 300 . the bulk of the battery mass ( e . g ., greater than 90 % of the battery mass ) may be present within the organism for a finite amount of time . the total amount of time that the battery 100 resides in the gi tract 300 may be , for example , 24 to 36 hours , but no longer than 5 to 7 days . for example , 90 % of the initial mass of the battery 100 may exist within the organism for a time period of less than 5 days , assuming normal digestive function of the organism . after this time period , the materials of the battery 100 are absorbed or metabolized , or passed through the gi tract 300 and eventually excreted . the materials of the battery 100 are selected such that they can be completely bioabsorbed by the organism or efficiently secreted without any negative health impacts . fig4 is a flowchart of operations performed by a water - activated , ingestible battery . as described above , the process 400 includes diffusing an electrolyte into an anode and a cathode of the battery following a dissolution of an outer casing of the battery ( 402 ). in some implementations , diffusing the electrolyte into the anode and the cathode may include dissolving the electrolyte contained in reservoirs within a cell casing of the battery . in some implementations , diffusing the electrolyte into the anode and the cathode may include passing the electrolyte through the cell casing . based on the diffusion of the electrolyte , the battery is activated ( 404 ). following activation , current is delivered a current across electrode leads of the battery ( 406 ). current is delivered across electrode leads by migrating cations infused in the anode from the anode to the cathode of the battery . the delivering of the current across the electrode leads may cause a powering of a medical device that is implanted in the organism that ingests the battery . after a predetermined time , the battery ceases to deliver the current across the electrode leads ( 408 ). following a cease in the delivery of the current , the battery is configured to degrade or break down . a number of implementations have been described . nevertheless , various modifications can be made without departing from the spirit and scope of the processes and techniques described herein . in addition , the processes depicted in the figures do not require the particular order shown , or sequential order , to achieve desirable results . in addition , other steps can be provided , or steps can be eliminated , from the described processes , and other components can be added to , or removed from , the describe apparatus and systems . accordingly , other embodiments are within the scope of the following claims .