Why does my phone battery drain faster in the cold?
The Real Answer
Your phone battery can appear to drain faster in the cold because low temperatures temporarily reduce how much power a lithium-ion battery can deliver efficiently. Cold slows electrochemical and ion-transport processes inside the battery and increases internal resistance, which reduces usable performance.
That can make the battery percentage fall faster than expected or cause the phone to shut down even though the battery would perform better at a warmer temperature. Manufacturers such as Apple explicitly note that very cold conditions can temporarily shorten battery life.
For ordinary cold exposure, much of that performance loss is temporary. As the battery returns to its normal operating temperature, its available performance can return as well. A cold-weather drop therefore does not automatically mean the battery permanently lost that amount of capacity.
Cold weather turns your battery percentage into a number you stop trusting. You pull the phone out for directions, watch the percentage drop, shove it inside your coat, then end up standing at the next crosswalk with the phone tucked under your shirt for warmth while you wait to ask it which way the restaurant is.
Why People Ask This
People ask because a battery percentage feels like a stored quantity that should not care about the weather. When the same phone suddenly loses usable runtime or shuts down in the cold, it looks as though charge physically disappeared. The missing piece is that lithium-ion battery performance itself changes with temperature.