Charge your mobile without an outlet

Very often there are situations when the battery on the phone is dead, and there is no socket at hand. Or, for example, you are going on a hike for several days, and you constantly need a work phone. Buying replacement batteries for your phone is expensive and unwise. But AA batteries are cheap and can be found in any stall. To make a device that charges your phone using regular batteries, you only need a piece of wire with a charging plug, a 2 ohm resistor and four AA batteries.