I suppose most of you don't have satellite phones and take normal cell phones when going outdoors. That's good, phone can be useful especially when one needs to call for help. The problem with phones is that they need energy to work. Energy comes from batteries. Batteries tend to exhaust. You see my point?

So remember: always recharge your cell phone batteries before going out. That's one thing. But it doesn't solve some other problems. Ok, but some may say "I'm going out only for couple of hours and I have charged my phone, what problems can I have?". Well, indeed todays batteries can keep our phone working for over a week. In normal conditions. Let's see what can shorten our batteries life time:

low temperature

lack of or weak signal - phone searching for signal consumes more energy

humidity

using the phone and running background applications (ie. GPS)

breaking or losing the phone

Those factors can drain your battery really fast. So what you should do is take a second phone with you. You should keep it turned off, packed in tight waterproof container and, especially if there's cold outside, keep it under your cloth close to the body.