"Use iOS devices where the ambient temperature is between 0º and 35º C (32º to 95º F). Low- or high-temperature conditions might cause the device to change its behavior to regulate its temperature. Using an iOS device in very cold conditions outside of its operating range may temporarily shorten battery life and could cause the device to turn off. Battery life will return to normal when the device is brought back to higher ambient temperatures."
( https://support.apple.com/en-us/HT201678 )
( https://support.apple.com/en-us/HT201678 )