Battery-optimized compensation system

Apparatus for use with a medical implant that comprises a receiving coil, the apparatus comprising:

• a housing configured to be placed against skin of a subject;
• a transmitting coil disposed in the housing;
• control circuitry comprising a power stage and configured to transmit power to the medical implant by activating the power stage to drive a current at a fixed frequency through the transmitting coil to induce an induced current in the receiving coil;
• a battery coupled to the housing and configured to power the control circuitry;
• a sensor configured to determine an indication of divergence of
• (i) a real-time resonance frequency of the transmitting coil, with respect to
• (ii) a reference resonance frequency of the transmitting coil;
• and
• one or more electrical components, coupled to the control circuitry,
• wherein:
• the control circuitry is configured to receive an input from the sensor indicative of the divergence and use the one or more electrical components to reduce the divergence by tuning the resonance frequency of the transmitting coil in response to the determination of the sensor.