This afternoon it happened to me,.... Damn empty battery and no charger for miles... At least that I know of.
So what do you do ? Build your own, in,.... 1 minute.
Step 1: Find the pinout of your phone
To find the pinout of your phone, you could use Google, or use ( the one I used, with help of google Pinouts ). Hit Ctrl + F and go look for you phone pinout. If you can't find it, you'll have a problem and won't be able to continue, but you usually will.
My phone has a 'standard ?' Sony Ericsson plug so it was easy to find. I used the image below, disgarding the Datacable part,... which it think can be pretty usefull :).