Why does my battery drain faster in cold weather?

A phone dying at 40% on a cold walk is alarming and almost always misread as a failing battery. The battery is fine; it is temporarily unable to deliver what the phone is asking for.

Safety

Step by step

1. Understand what cold does.Lithium batteries work by ions moving through an electrolyte. Cold makes that fluid more viscous and the movement slower, so internal resistance rises and the battery cannot supply current as easily.
2. Know why it shuts down suddenly.Voltage sags under load in the cold. The phone reads the sag as an empty battery and shuts down to protect itself, which is why it drops from 40% to nothing rather than gradually.
3. Expect it to recover.Warm the device up gradually and the charge usually comes back. That recovery is the proof it was temperature rather than a failed battery.
4. Keep it against your body.An inside coat pocket rather than an outer one or a bag. Body heat is enough to keep it in its working range in most British weather.
5. Use a case.Any case adds insulation and slows the temperature drop. It makes a genuine difference on a cold day out.
6. Never charge it while very cold.Charging below freezing plates lithium metal onto the anode, which permanently reduces capacity and can create an internal short. Let it warm to room temperature first.
7. Warm it gradually.In a pocket or a warm room. Not a hairdryer, radiator or oven — rapid heating causes condensation inside and stresses the battery and screen.
8. Reduce what it is doing.High load makes the voltage sag worse. Turning down the screen, closing navigation and using low-power mode all reduce the current demand.
9. Carry a power bank in the same inside pocket.Keeping the bank warm matters as much as keeping the phone warm — a cold power bank delivers poorly too.
10. Tell temporary from permanent.Poor performance only in the cold is normal. Poor performance in the warm as well, or a battery health figure well below 80%, is a battery at the end of its life.
11. Watch for condensation.Bringing a very cold phone into a warm room can condense moisture inside. Let it warm gradually in a bag rather than straight onto a radiator.
12. Take it seriously on a hill.If the phone is your map or your way of calling for help in cold conditions, carry a paper map and keep the phone warm and off. This is a safety matter rather than an inconvenience.

Tips

• Inside pocket, not outer pocket. It is the whole fix for most people, and it costs nothing.
• Do not charge a freezing phone. Let it reach room temperature first — charging cold causes permanent damage.
• If it only misbehaves in the cold, the battery is fine. Cold plus warm poor performance is a replacement.

Common mistakes

• Charging a phone straight from the cold — Charging a lithium battery below freezing plates metallic lithium inside it, which permanently reduces capacity and can create an internal short.
• Warming a phone quickly on a radiator — It stresses the battery and condenses moisture inside the case. Warm it gradually in a pocket instead.

If it doesn't work