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The Cold Truth about Phone Batteries

Your battery indicator doesn't always tell you the truth.

Paul Bodnar       Tech on the Trail       05/09/2019
Paul Bodnar
Tech on the Trail
05/09/2019

Long-distance backpackers experience a wide range of temperature. Which means that if you carry a phone, your phone also experiences a wide range of temperature. We have noticed a lot of confusion about how low temperature affects your phone’s battery life, so we decided to run an experiment and check it out.

But first, what is the acceptable operating temperature range? Apple recommends a range of 32º – 95ºF (0º – 35ºC) for the iPhone and Google recommends the same for its Android Pixel 2. You should turn your phone off if you are going to be outside this temperature range.

Battery level of a cold phone

We ran an experiment on an iPhone 6+ to see what happens to battery level when your phone is cold. Here is what we did:

  1. Put an 85% charged iPhone in a 36ºF / 2ºC refrigerator for 11 hours with power ON
  2. After 11 hours the battery level is 27%
  3. Warm the phone to room temperature and the battery level is still 27%
  4. Restart the phone and the battery level is 71%*

*The temperature discrepancy appears to be a bug in the iPhone 6+, which has since been corrected in newer models of the iPhone, i.e. when newer iPhones warm up, the battery level is reported correctly rather than staying at it’s cold-temperature level.

These results are as expected — a battery works with a chemical reaction, and chemical reactions slow down when it’s cold. So your phone is tricked into thinking there is less battery capacity, when in reality, the stored energy has not changed (read this for a full explanation).

iPhone 6 Plus cooled down to 36 degrees Fahrenheit in a refrigerator.

Recommendations

  • Turn your phone off if the temperature is higher than 95F/35C or lower than 32F/0C
  • If your phone is cold and you need to use it, warm it up in your pocket before you use it so that you know the true battery life.

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About the Author
A man wearing an Arizona Trail baseball cap stands in a field in front of a mountain.

Paul Bodnar

Paul has always liked hiking and thru-hiked the Pacific Crest Trail in 1997 after college. After years of working in chemistry, he wanted to create a career involving the outdoors, so he hiked the Pacific Crest Trail again in 2010 to do research for his guide book Pocket PCT. He realized that creating a smartphone app for navigating the outdoors would make it easier to keep the data current and provide a better way to navigate. While hiking with Ryan (aka Guthook) in 2010, they decided to work together to create the first comprehensive smartphone guide for the Pacific Crest Trail. Now with the help of a team of great people they have created over 50 guides for trails around the world.