Techniques for transcutaneous transferral of energy to an implantable medical device are disclosed. An embodiment includes a system comprising an implantable medical device having a secondary coil. An external device is provided to transcutaneously transfer energy to the secondary coil. The external device comprises a housing having a side adapted to be positioned in proximity to the secondary coil when the external device is transferring energy to the secondary coil. A temperature sensor is coupled to the side to determine a temperature indicative of heat to which the patient is being exposed during the transfer of energy. A control circuit is adapted to control the transfer of energy to the secondary coil based on the temperature. For instance, the control circuit may limit transfer of energy by controlling times at which transfer of energy occurs or controlling an amplitude of a signal within the external device.