If you've ever had a hunch your phone's charge doesn't last as long in the wintertime, you're not crazy: Cold temperatures have a nasty effect on batteries.
The scientific explanation for this lies in how batteries work. Basically, their job is to store chemical energy until you need them to power or charge your device. Then they go about converting that chemical energy into electrical energy. However, cold weather causes internal resistance, slowing down the conversion process and resulting in less overall capacity. The kinds of batteries used in most phones are particularly vulnerable to this effect.
Translation? Just like wintertime makes it harder to get your car to start, your phone won't last as long in cold weather. However, all is not lost — there are some ways to keep your phone as warm and happy as a skier sipping hot cocoa after a day on the slopes.
First, keep your phone as close to your body as you can. Take it out of your backpack or purse and stick it in your jeans or, better yet, in the inside pocket of an insulated base layer. That'll help your body heat keep things warm. Second, consider picking up an insulated case. These can be a little on the bulky side, but it's better to have a cumbersome case than a dead phone.
And finally, avoid taking your phone out in really frigid temperatures — the ambient air will suck out your phone's heat quicker than you can send a text to Mom.