For supplying energy to a medical implant (100) in a patient's body a receiver (102) cooperates with an external energizer (104) so that energy is wirelessly transferred. A feedback communication system (109) sends feedback information from the receiver to the energizer, the feedback information being related to the transfer of energy to the receiver. The feedback communication system communicates using the patient's body as an electrical signal line. In particular, the communication path between the receiver and the external energizer can be established using a capacitive coupling, i.e. the feedback information can be capacitively transferred over a capacitor having parts outside and inside the patient's body. An energy balance between the amount of energy received in the receiver and the energy used by the medical implant can be followed over time, and then the feedback information is related to the energy balance.