It was a summer night about a year ago, the power was out and it was getting hot. We had battery-powered fans in the house somewhere, but we didn't remember where they were and didn't want to get hotter looking for them. That's when it hit me, I have tons of computer fans in a box, why not use one of those? I grabbed a good-sized one and my original Gameboy (the one that uses 4 AA batteries), I took the wires from the fan and stuck them between the main contacts (the ones that go to the board) and the batteries, and with a little push-start, the fan worked.
Granted it was only 6 volts of power to a 12 volt fan, but it sure felt good to have it. A few months later, I decided to make my own battery-powered fan just in case this ever happened again. I started with a 7x7x2 inch flip-top cardboard box, a ~3 inch diameter PC fan, and two 6 volt batteries.
The first time I built it, it was switched on by touching two wires together and the box had about five square holes cut into it for ventilation, and everything was held together by duct tape, cotton string, and bread ties (the wire ones). Since then, it's gone thru 4 revisions to improve air flow and safety.
The first revision I did was a very simple one, I added a spring to keep the wires together. Next revision I added ducting and trimmed the box around the fan to improve airflow, and it REALLY made a difference (think low to medium speed on a normal fan). Then came a 3-way toggle switch for the power. Finally, I swapped out the toggle for a standard 2-way switch about 2 or 3 months ago.
That's enough of all that explaining, it's time for pictures!: