Hi @danj, I guess I was not able to describe it the way that you can understand it.
This question is just not about a termal issue, really.
Even if I start the computer from a dark sleep in the morning and battery charge is 33% without being connected to a charger, the battery charge level will drop as soon as it reaches something about 30%. Then it will drop to 7% within 10 minutes, even with a cold battery.
If It is charged at maybe 90% (and disconnected from the charger) it will take 1 hour in use to get it to 70% charge level - without being connected to a cable. Just the charge level of the battery. So around 20-25% charge level per hour.
I can use the battery for about 4-4.5 hours.
So there is no heat, there is no charging. It is about the battery delivering it's power.
If the battery has only 30% charge left, it will drop quite fast to 7% and lower. It has nothing to do with heat. It deals with the discharging speed of the battery solely.
So either the battery is bad or the communication between the mainboard and the battery chip with regards to it's real charging status.