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. In one example, a temperature sensor may sense a temperature of a portion of a device, wherein the portion is non-thermally coupled to the temperature sensor. A processor may then control charging of the rechargeable power source based on the sensed temperature.