Daniel Sherwood, left, and Paul Guzyk in a Pruis that they modified to run on battery power alone.

Paul Guzyk and Daniel Sherwood are computer geeks who co-founded 3Prong Power, a Berkeley business that transforms standard Toyota Priuses into all-electric green machines.

In 1999, Guzyk moved to California and rediscovered an old passion for cars after tinkering with a Prius. He found that in many ways the Toyota hybrid was more like a computer than an automobile. Notably, it ran on recognizable computer standards similar to those found in an office network.

"I found that modifying the Prius is like getting your computer to do what you want it to do," says Guzyk.

In 2006, he met fellow Prius tinkerer Sherwood. Together they gave a 2004 model an all-electric makeover.

First, they installed a bank of Prius batteries they had salvaged from a junkyard. That didn't work well, so they tried traditional lead-acid batteries, used in electric wheelchairs, which did the trick.

Next, they developed software that programmed the Prius to run only on its newly enlarged battery pack. Unlike the one in an unmodified Prius, the car's internal-combustion engine doesn't fire up -- and burn gas. Presto: instant electric car, albeit one with a range of only about 25 miles.

In 2007, they launched their startup in a former Cadillac dealership with less than $100,000 of their own money. Since then they've added six employees and now expect to do 500 conversions, or some 40 a month, through 2010; at $4,500 per job, that works out to about $2.2 million in annual sales.