I got out my geeky Christmas tree this year and decided that I did not want to waste another nine volt battery on the tree this year. So I created a 9 volt battery that connects to the USB port on your computer for power.

1) print the battery case
2) glue a nine volt battery connector to the top of the battery case sending the wires through the holes on the top of the battery. (note if you steal a connector from an old electronic device be careful that the wire colors may be backwards. Check the outputs with a voltmeter before use)
3) find an old usb cable and cut off the end that does not connect to the computer.
4) inside the outer wire are typically 4 wires the red wire is the positive voltage and the black wire is the negative voltage. (verify this with a voltmeter, these will only be 5 volts coming from the computer.)
5) stick the usb wire through the hole in the side of the battery case.
6) with the wires in the battery case twist together the black wire from the USB wire to the negative wire from the 9 volt battery connector.
7) get a 9 volt booster from Pololu (http://www.pololu.com/product/2116) or similar from another site.
8) solder the black wire twisted with the negative wire from the battery plug to the center connection on the Pololu voltage booster.
9) solder the positive wire from the battery connector to the voltage out connection on the pololu voltage booster.
10) solder the red wire from the USB wire to the volt in connector on the pololu voltage booster.
11) push all of the wires inside the battery case until it looks good.
12) plug into the computer or wall wart and enjoy an endless 9 volt battery.
Note: This could damage any electronics involved if done incorrectly.