I have been experimenting with my own EC source code.
Now that I have stopped the battery doing mini charge/discharge cycles, the battery stays a lot cooler during use, when I have the PSU plugged in.
The touchpad seems to stay a lot cooler.
I have also now implemented support in the EC to tell me what the battery temperature is.
The battery on the FW16 has an internal temperature sensor that is not reported anywhere else. I assume the FW13 is similar.
The battery temp sensor seems to be more accurate than me touching the touch pad to find out how hot the battery is. 
There is limits set for how high the battery can get, and if too hot, it will prevent charging and discharging.
In the EC source code:
./chromium/src/platform/ec/zephyr/dts/bindings/battery:
atl,framework55w.yaml ← The FW13 55W battery charge max = 55 C, discharge max = 70 C
atl,framework61w.yaml ← The FW13 61W battery charge max = 55 C, discharge max = 70 C
atl,framework85w.yaml ← The FW16 85W battery charge max = 55 C, discharge max = 70 C
When I search about Lithium Ion batteries, it tends to say that damage start when charging / discharging > 30 C, but I don’t know what evidence there is for that.