Hi, my new S9 plus with all apps closed, just gsam to see battery temperature in the windshield car support gets 47 Celsius. It's extremely hot for a phone or not? It's currently 25 Celsius outdoor. I can't remember a phone who gets so hot in this condition. Tried restarting also.
I would say that is too hot, try running the same test with your phone without the phone being exposed to sunlight. Any device that holds batteries should never be exposed to direct sunlight for obvious reasons even on a cloudy day a windscreen can amplify heat from the sun. Try running a game with a high graphics requirement indoors and then test the temperature, i would say the upper limit without heat exposure would be a maxinum of around 40 celsius any more than that and i would advice getting the device looked at. If the results are normal i would say you need to adapt your windscreen holder or reposition it next to a pillow to shade it from the sun as much as possible.
Temperature can be effected by the following:
Heavy usage and multiple backround processes
Backround services such as GPS, BLUETOOTH, SYNC etc
And so on.
Incorrect charger or incorrect charging.
And much more
You might need to wipe the cache partition, possibly some old file(s) could be cause of the problem, here is what resolved the problem on my S6 what will probably work for you too:
Noticed for several months that phone was turning very hot to the touch (especially the part above the power button).
What I did to resolve:
Turn of the phone completely by holding the Power Butten and selecting turn off.
Press and keep pressing together the following buttons:
Do this until "Samsung" appears on the phone, then wait and eventually a menu will apear.
Make very sure you select the following option by using the VOL + - buttons:
Wipe Cache Partition (This option does not delete any apps nor user data of your phone), confirm and restart according the instructions displayed on your Terminal. (Confirm using the power button)
Then reboot the phone by selecting the correct option. (Reboot system).
Phone will restart, initally some apps might take a bit longer to start which makes sense as the cache was emptied.
Good luck, hope it helps solve the problem for you too!