I wanted to make it as simple a possible so I decided to use 4 AA sized NiMH batteries rated at 1.2v (or 1.25v) Which can provide the needed 5v without regulation. This also makes it possible to more quickly charge PSP's which can draw almost 1A when charging.
To extend the functionality I decided it should also be a flashlight. But a quick search of the local stores showed that most AA flashlights are generally 1 or 3 cells. Fortunately for me I decided to check the bike aisle at Wal-Mart and found that many of the bicycle headlights are 4AA cell!
So using a bicycle headlight we'll end up having a:
1. portable USB power
3. bicycle headlight
Not only that but I happened to have a Luxeon III star and optics laying around the house so, why not improve this project by switching out the bulb for the Luxeon?
Expandable Capacity Bicycle Headlight
The most interesting part for me is that if you decide to make a second battery pack and connect them together via USB you'll double the burn time of the flashlight! How cool is that when being used as a bicycle headlight?!?
How about connecting it to a USB power generator such as the Hand Crank Lego USB charger set up so it's turned by a tire?
Multipurpose enough? I think so.
Step 1: Parts
-1 Bicycle headlight (4xAA type)
-4 rechargable NiMH AA batteries
-1 Luxeon III star
-1 Luxeon Optics
-1 Heatsink for Luxeon (I used a copper pipe cap)
-1 Resistor ( Luxeon resistor calculator )
-1 USB motherboard adapter
Where to find parts
I didn't have to buy a headlight but they can be had at the bicycle section of most stores.
NiMH batteries. Again I had these as well as a charger. I got them from Walmart. They are 2500mAH generic, $5 at in the electronics section. I think they had it also availible with a wall charger for a bit over $10. Either way they're half the price of the brand names.
I don't remember where I got the Luxeon III, somewhere online with the optics and resistor. I believe everything cost about $10 shipped. I would suggest using either 5 or 10 degree lens.
The USB motherboard adapter I got from ebay for $2 plus $2 shipping