Example embodiments of an implantable device are configured to be implanted within a patient to provide medical therapy to the patient. In general, an implantable rechargeable device includes a rechargeable battery and an electronic board assembly arranged within a case and an antenna electrically coupled to the rechargeable battery. The antenna is configured to receive power and to transfer at least a portion of the received power to the rechargeable battery for recharging. A phase change material is arranged within the case around at least a portion of the electronic board assembly. The phase change material is configured to transition from a first phase to a second phase at a transition temperature when the insulating material absorbs heat (e.g., from the electronic board assembly).