Devices, systems, and techniques for monitoring the temperature of a device used to charge a rechargeable power source are disclosed. Implantable medical devices may include a rechargeable power source that can be transcutaneously charged. The temperature of an external charging device and/or an implantable medical device may be monitored to control the temperature exposure to patient tissue during a charging session used to recharge the rechargeable power source. In one example, a temperature sensor may sense a temperature of an internal portion of a device, wherein the housing of the device is not directly thermally coupled to the temperature sensor. A temperature for the housing of the device may then be estimated based on the sensed temperature provided by the non-thermally coupled temperature sensor. A processor may then control charging of the rechargeable power source based on the determined temperature for the housing.