system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why do smart phones shut off in cold weather before they’ve reached 0% battery?

Recently I’ve been out in the cold and my iPhone has shut off with about 40% battery remaining. Is this a simple answer such as it’s too cold for electrons to flow in the battery?
gpt
I'll provide a brief answer.

Phones today are powered by lithium-ion batteries. They rely on the flow of ions (something like electrons, except bigger, slower) through an oily-gel like material (makes them even slower!) across two 'plates' as they discharge to power the phone.

When it gets cold, it gets harder to move (just as you'd find it harder to move in the cold) and after a certain threshold, the battery just seizes up and ions just don't move fast enough to provide enough current for the phone. The phone shuts down.

This threshold temperature is rather cold, in the -30 ~ -40 C. but depending on the battery, conditions that you were out in, initial conditions and whatnot, you may see it shut off at relatively warmer (~ -20 C) temperatures as well.