A method for controlling wireless transmission of energy supplied to an electrically powered medical device when implanted in a patient, the method comprising powering the medical device by an internal energy receiver of the medical device, wirelessly supplying energy to the internal energy receiver by an external energy source located externally to the patient, wherein the external energy source is equipped with a primary coil from which the external energy source inductively transmits said energy to a first secondary coil in the energy receiver, the method further comprising determining, by measurements, one or more parameters related to a first coupling factor (Cl) between the primary and the first secondary coil, transmitting, by the external energy source, a first amount of energy to the energy receiver for enabling detecting, by the medical device, information related to the first coupling factor, wirelessly sending, by the medical device, feedback information related to said first coupling factor to the external energy source, receiving, by the external energy source, said feedback information from the medical device, performing, by the external energy source, a predetermined action based on: said feedback information and at least one of: letting the first secondary coil be substantially without electrical load when measuring the first coupling factor, wherein the energy receiver comprises an electronic component connected to the first secondary coil for enabling and disabling the flow of electrical current between the first secondary coil and the medical implant, and providing an electronic component connected to a second secondary coil comprised in the energy receiver, the primary coil having a second coupling factor in relation to the second secondary coil, said second secondary coil being used to supply information related to the second coupling factor, the second coupling factor having a predetermined relation to the first coupling factor, wherein the electronic component is configured for preventing or substantially reducing the flow of electrical current between the second secondary coil and the medical implant during the measurements of parameters related to a second coupling factor. powering the medical device by an internal energy receiver of the medical device, wirelessly supplying energy to the internal energy receiver by an external energy source located externally to the patient, wherein the external energy source is equipped with a primary coil from which the external energy source inductively transmits said energy to a first secondary coil in the energy receiver, the method further comprising determining, by measurements, one or more parameters related to a first coupling factor (Cl) between the primary and the first secondary coil, transmitting, by the external energy source, a first amount of energy to the energy receiver for enabling detecting, by the medical device, information related to the first coupling factor, wirelessly sending, by the medical device, feedback information related to said first coupling factor to the external energy source, receiving, by the external energy source, said feedback information from the medical device, performing, by the external energy source, a predetermined action based on: said feedback information and at least one of: letting the first secondary coil be substantially without electrical load when measuring the first coupling factor, wherein the energy receiver comprises an electronic component connected to the first secondary coil for enabling and disabling the flow of electrical current between the first secondary coil and the medical implant, and providing an electronic component connected to a second secondary coil comprised in the energy receiver, the primary coil having a second coupling factor in relation to the second secondary coil, said second secondary coil being used to supply information related to the second coupling factor, the second coupling factor having a predetermined relation to the first coupling factor, wherein the electronic component is configured for preventing or substantially reducing the flow of electrical current between the second secondary coil and the medical implant during the measurements of parameters related to a second coupling factor. letting the first secondary coil be substantially without electrical load when measuring the first coupling factor, wherein the energy receiver comprises an electronic component connected to the first secondary coil for enabling and disabling the flow of electrical current between the first secondary coil and the medical implant, and providing an electronic component connected to a second secondary coil comprised in the energy receiver, the primary coil having a second coupling factor in relation to the second secondary coil, said second secondary coil being used to supply information related to the second coupling factor, the second coupling factor having a predetermined relation to the first coupling factor, wherein the electronic component is configured for preventing or substantially reducing the flow of electrical current between the second secondary coil and the medical implant during the measurements of parameters related to a second coupling factor.