If you feel like your HTC One is overheating and want to check its battery temperature, there is an easy and fast method to do so. Just go to Phone and dial *#*#4636#*#*. A Testing page will show up.
Then tap Battery Information and you will have all the info you need.
You can check the battery health, temperature, voltage, scale, technology etc. If your battery temperature is more than 40°C then it’s overheating.
In this case lowering the CPU & GPU voltages and under clocking with 200 or 300 mHz would do the trick.