I got my M8 up to almost 140F the other day in my windshield mounted car dock. I use Car Home Ultra as my car dock app and it shows the temp (for the battery I think) under the charge level, but I noticed it because my charging LED was flashing amber instead of solid amber. So I diverted my A/C through my defroster vents to hit the phone and it cooled it down to under 100F in a few mins. It started charging normally again once it got under 120F, so that's good to know, I guess, hah.
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