A medical system comprising internal parts for implantation in a patient and external parts for use externally to the patient, the external parts comprising an energy source equipped with a primary coil for inductively transmitting energy to the implantable parts and an external control unit for the control of the energy source, the internal parts comprising an electrically powered medical device, an energy receiver equipped with a secondary coil for inductively receiving energy for the medical device from the external energy source and an internal control unit for the control of the internal parts, in which system the internal control unit is arranged to wirelessly transmit feedback information to the external control unit, the system being arranged to determine said feedback information based on or relating to a parameter.
