Erm...you can't. Unless you had one of those emergency phone battery chargers, I use them sometimes for when I go camping for long periods of time, they fill about half the battery.
You mean those battery operated chargers? I got one of those compatible with almost any mobile phone that exist, in my car. Got it at work. But never had to use it. i'd say it's the best solution, or you can take out your sim and ask for someone to lend your his phone
There are battery loaders available that work on solar power. They aren't cheap but in case of a true emergency I think you were glad you bought one. Can I show links if you PM me about this? If so, I'll be happy to show you where you can mail order these tools.
may sound stupid but it works temporarily rub on the battery for like 5 minutes or so i used to do it with my old nokia when it would cry that it was low battery id turn it off and rub my index and middle finger on it for several minutes