If you live in a cold place, and put the phone in the cup holder or in the passenger seat or something, the temperature is often enough to kill it because the battery loses 'influence' when the temps are that low. I live in Winterpeg and it's -25C outside most of the time in the winter. In the car, if I put my phone in the cup holder, if the battery is 40% or less, it sometimes dies or drops in charge if it sits in the cup holder for long, as it's not a particularly heated area. The phone having a metal frame and backside is to blame for this. If you warm it up again by holding it in two hands and using your hands' warmth, it should regain 'influence' (not the correct word but you get the point) from the battery. That's probably what's going on right now with your phone.