unexpected iPhone shotdown at 30-40% battery in cold conditions

Hello Apple Support,

i'm a runner and run on cold/rainy days too. Since the last cold/rainy days i've got the problem, that my iPhone 6 will be shutdown

on 30-40% battery life unexpected. If i try to start it again, it shows the icon to put it on power.

After waiting a little bit i can start the iPhone, can see battery with 30% for example and a jump to 7% for example.

Few minutes later it turn off again. Or if i start camera app or something like this it turn's off again on this weather conditions too.

I put the iPhone in my jacket, it's not wet from rain but very cold.

Please help, it's unusable in this condition and i've got no problems like this with my other iPhone generations before.

best regards

Frederic