As long as the radio is turned on, the battery does not charge, so the radio will stay reasonably cool if you set it not to charge. If you turn the power off and leave the USB power coming in, the battery will start to charge, which causes the most heat in the radio. I found if you put the display brightness above maybe 40%, the radio seems to run warmer also. I leave mine at 20% running 24/7/365 and it is cool to the touch.