Recently took my iPhone 6S as my primary shooter on a vacation. Temperatures ranged from 34 deg F to 41 deg F. Without fail, when my iPhone got to near 40% battery, the phone would shut down and show the charge indicator (the plug graphic on the screen). After the phone warmed up (or I plugged it into a small, portable power bank), the phone revived and was back up to bear 40% where it left off. Very frustrating. In normal daily office use, I am able to use my phone all the way down to 0% charge.