I have a very handy cordless electric screwdriver, it operates at 5.4 v DC and can usually manage about 50-75 light-duty screws before needing a top-up. Doesn't sound much, but this thing has no batteries, instead it has a capacitor that takes only 90 seconds to fully charge from a completely dead state. It also had quite high torque for its driving duties. Here's. 2008 review of the thing: http://www.onlinetoolreviews.com/reviews/gmcfastcellscrewdrivers.htm, mine being the higher-capacity straight barrel design.