Abstract: Aspects disclosed in the detailed description include an ingestible power harvesting device and related applications. An ingestible power harvesting device includes a cathode electrode and an anode electrode that can catalyze a power generating reaction to generate a direct current (DC) power when surrounded by an acidic electrolyte. The cathode electrode and the anode electrode are coupled to an encapsulated electronic device that includes power harvesting circuitry configured to harvest the DC power and output a DC supply voltage for a prolonged period. In examples discussed herein, the prolonged period is at least five days. The DC supply voltage powers an electronic circuit in the encapsulated electronic device to support a defined in vivo operation (e.g., controlled drug delivery, in vivo vital signs monitoring, etc.). As such, the ingestible power harvesting device can operate in vivo for the prolonged period without requiring an embedded conventional battery.