An ingestible event marker comprising: a battery section including two electrodes configured to supply a battery voltage upon contacting a body fluid by generating a current between the two electrodes using the body fluid as a conductive medium; and an integrated circuit configured to store an identification code; wherein the IC comprises: a transmission switch transistor; a control logic configured to control an impedance between the two electrodes to alter the current flowing through the body fluid to transmit a coded signal representing the identification code by switching on and off the transmission switch transistor; a power supply circuit coupled to the control logic; a capacitor coupled to the control logic, the battery section, and the power supply circuit, the capacitor being configured to be chargeable by the battery voltage: and a local oscillator; the ingestible event marker being characterized in that the power supply circuit comprises a recharge transistor and a recharge-protection diode, and wherein: when a level of charge stored within the capacitor is below a predetermined threshold, the control logic is configured to generate a recharge signal, and the recharge transistor is configured to couple the battery voltage to the capacitor and to recharge the capacitor based upon the recharge signal. a battery section including two electrodes configured to supply a battery voltage upon contacting a body fluid by generating a current between the two electrodes using the body fluid as a conductive medium; and an integrated circuit configured to store an identification code; wherein the IC comprises: a transmission switch transistor; a control logic configured to control an impedance between the two electrodes to alter the current flowing through the body fluid to transmit a coded signal representing the identification code by switching on and off the transmission switch transistor; a power supply circuit coupled to the control logic; a capacitor coupled to the control logic, the battery section, and the power supply circuit, the capacitor being configured to be chargeable by the battery voltage: and a local oscillator; the ingestible event marker being characterized in that the power supply circuit comprises a recharge transistor and a recharge-protection diode, and a transmission switch transistor; a control logic configured to control an impedance between the two electrodes to alter the current flowing through the body fluid to transmit a coded signal representing the identification code by switching on and off the transmission switch transistor; a power supply circuit coupled to the control logic; a capacitor coupled to the control logic, the battery section, and the power supply circuit, the capacitor being configured to be chargeable by the battery voltage: and a local oscillator; the ingestible event marker being characterized in that the power supply circuit comprises a recharge transistor and a recharge-protection diode, and wherein: when a level of charge stored within the capacitor is below a predetermined threshold, the control logic is configured to generate a recharge signal, and the recharge transistor is configured to couple the battery voltage to the capacitor and to recharge the capacitor based upon the recharge signal.