http://www.popsci.com/diy/article/2008-02/make-instant-charge-screwdriver
Also useful links herein... see tools, portable use section
http://en.wikipedia.org/wiki/Electric_double-layer_capacitor
Coleman FlashCell - came and went...
http://www.popularmechanics.com/technology/gadgets/4223118
Supercapacitor screwdriver comes up as a half baked idea...
http://www.halfbakery.com/idea/Supercapacitor_20Cordless_20Screwdriver
There are problems:
- Low voltages
- Series cell balancing issues
- Brief (millisecond) blips in charging voltage can do damage
- Linear capacity means energy in under 1V range goes forever unused/wasted
- Fast self discharge
