It was hot here yesterday, 101 degrees. My P4 was in a large black plastic carrying case in the back of the vehicle and sometimes in the sunlight. Batteries were fully charged to 100% for evening or next morning flight.
Decided on next morning at 5:30 AM as it was too hot in the PM. When I opened the black case in the morning, I could feel the heat coming out of it even though it was overnight in the garage at 70 degrees. The batteries were warm to the touch still, maybe 95 degrees.
When I got the P4 ready, I noticed the charge was already down to 78% from 100% the day prior. Heat seems to affect the Li-Po's in a downward number. Flight time was only about 8 minutes too before the RC began beeping to come home.
I thought the black case with foam would insulate it from the heat, but it seems to also insulate the case from cooling down as well. Heats up faster than it cools down maybe. Too bad the cases are not white as most seem to be black, and some blues too.