If your smartphone is exposed to the cold, the battery will drain faster.
Whenever possible, keep your phone charged so that you will have power when you need it. It is also handy to keep a car charger in the phone case for if your vehicle should get stuck in snow or on ice.
If your Smartphone has been exposed to the cold for a long time, you shouldn't use it right away. Instead, leave the phone to warm up to room temperature. If you boot your phone while it is cold, you could potentially damage the hard drive.
Whenever you are outside in cold temperatures, it is best to keep the phone on you. If you leave your phone inside of your car, the decreased temperature can cause damage to the sensitive components. If you have to keep your phone in the car, wrap it in a sweater or jacket.