Always on when connected to an external power source, otherwise a timeout

When the phone is connected e.g. to my car`s supply, I want the map visible all the time.

When I`m walking in the "wilderness" I switch the display on just to check the map for brief periods. But sometimes the phone turns on accidentally in my pocket and drains the battery.

So I would like to have a timeout after which the display turns off in my pocket. If I hit the on/off button the map shall be displayed (not the lock screen).

So there should be settings

"always screen on when external supply, on batteries a timeout of xxx seconds"