A body-mountable device includes an electrochemical battery configured to provide power when exposed to an aqueous fluid. The aqueous fluid could be blood, sweat, tears, or some other bodily fluid. The electrochemical battery includes an anode that includes zinc metal and is configured to provide an electrical potential relative to a cathode when the anode and cathode are exposed to oxygen and an aqueous fluid. The electrochemical battery could provide power to electronics configured to measure a physiological parameter at a plurality of points in time, to record such measured parameters, to transmit such measured parameters to an external system, or to perform some other functions. Components of the body-mountable device could be embedded in a polymeric material configured for mounting to a surface of an eye. Components of the body-mountable device could be disposed on a flexible substrate configured for mounting to a skin surface.
