Alright so I never really thought of the practicality of a portable charger until today. So I built one in the last half hour. It works with my MPx. Anyways, according to some threads, I found people getting many times more hours out of the external charger than the battery. So let's get at it.
First, a parts list. Now in this one I will be using the 4 AA battery pack, though it is just as easy to make it with the 4 AAA pack or even a 9V battery.
Parts needed:
Some kind of portable power source:
4 AAA Battery pack:
http://www.radioshack.com/product/in...entPage=family
OR 4 AA Battery pack:
http://www.radioshack.com/product/in...entPage=family
OR 9V Battery clip:
http://www.radioshack.com/product/in...entPage=family
7805 Power regulator:
http://www.radioshack.com/product/in...entPage=search
USB End
I usually get these from tearing apart free usb hubs I pick up at conventions, cause they're all usb 1.1
Some wire
Soldering skills
Pin layout for 7805:
Pins for usb:
So if we're working from the pics, then the wiring is straight forward.
Instructions:
1) Connect the red wire from your battery pack to the input pin on the 7805.
2) Connect the black wire from your battery pack to the Common on the 7805.
3) Connect the output pin of the 7805 to Pin 1 on the USB end.
4) Connect the Common pin of the 7805 to Pin 4 on the USB end.
And that's it!
Post pics if you made a creative case!
*EDIT*
Although mine charged fine, some of yours may require it to be on that "CONNECTED" screen to actually see it charging. In order to see this, connect pin 4 on the USB end to pins 2 and 3 on the USB end.