Heat and battery issue on a iMX8MP pocket reform

What temperatures does your OS see?

Here a photo of the “good” backplate:

And this is how the bad backplate looks like. For that one, the copper sheet extends throughout the whole plate and that kills wifi reception (but should have little influence on thermals): Wifi dropping constantly - #17 by DavePolaschek

Is that two hours until the system hard-shuts off or two hours until the battery meter shows 5% and you (or your OS) shuts down for safety and not to loose data?