iPhone 6 turns off when cold.

Hey there!

i was outside, it was like -3 to -4 degrees celsius.

i took my iphone out of my pocket, wanted to do something in safari when it randomly turns off!

i even had about 25% battery left. i could not switch it on again.

this is really annoying, and i haven't had this problem last year when it was cold.

my iphone 6 is becoming a year old in december

thanks in advance,

luca