Pat Cadam describes driving a plug-in hybrid electric vehicle as a “;funny sensation.”;

He says this as he whirs down King Street toward Ward Avenue in a white Toyota Prius, the engine only kicking over to gasoline power as he speeds past 35 mph for a moment.

In the back seat, Carlos Perez of Hawaiian Electric Co. has just recalled his first turn in a hybrid car, one of the utility's seven Prius vehicles on Oahu.

“;It really grows on you,”; Perez said. “;It's just like 'Wow.' It's amazing how you really embrace it.”;

It's the ultimate test drive, with each of the 11 minutes of 1.4 miles traveled sent wirelessly to a tracking system for analysis on how the car and battery perform.

Cadam is in Honolulu this week from San Francisco, where he runs a company called Green Gears that retrofits plug-in hybrid vehicles with complex battery systems more than four times as powerful as the 1.2-kilowatt-hour unit that comes in the car.

As of yesterday, the three-man team had converted four Prius vehicles on Oahu, one each operated by HECO, the University of Hawaii, the state and the U.S. Air Force, as part of a national effort to study the feasibility of plug-in hybrid electric vehicles. Tomorrow, Cadam will have finished another two cars on Maui belonging to the county and Maui Electric Co.

“;You throw a lot of your old assumptions out the window when you are driving one of these,”; Cadam says. “;People are still afraid that they need to have a car that will take them three times around the island.”;

Nationally, 80 percent of drivers travel 20 to 30 miles a day, most at less than 40 miles an hour. Given its below-average speed limits, Hawaii could see an additional boost in miles per gallon, said Jim Francfort of the Idaho National Laboratory, which is under a one-year agreement to compile the data.

“;The islands make a very unique operating atmosphere,”; he said. “;The temperature, the terrain, there's traffic. You see more shorter drives here.”;

Regular Prius models, which sell for $22,000 to $28,000, get 40 to 45 miles a gallon depending on how aggressively they are driven - they switch to gas use when traveling above 35 mph.

When adding the A123/Hymotion 5-kilowatt-hour battery, a driver can expect 80 to 95 miles a gallon. Each battery operates on 50 percent to 70 percent of the charge, taking the driver about 40 miles using both gas and battery power. After a battery is spent, the engine switches to the car's 11 to 12 gallon gasoline tank. A driver can then plug the battery, which is estimated to last a decade, into a standard 120-volt wall outlet for charging.

“;There is no more sensible way in the foreseeable future to go than electric vehicles,”; said HECO spokesman Peter Rosegg, who added that the utility is interested in learning how the plug-in hybrid conversion here compares to studies performed on the mainland that have shown there can be increased fuel economy with the vehicles, even when considering the cost of electricity.

The utility has tested electric vehicles before - from 1994 to 2004 it had about a dozen of them until General Motors abandoned the program. Separately in December, Palo Alto, Calif.-based Better Place proposed a $1 billion plan to be funded through private investments that would include up to 100,000 charging stations around Hawaii and possible state incentives for thousands of electric car buyers to be rolled out in the next several years.

There are about 300 vehicles nationwide running on similar A123/Hymotion lithium-ion batteries, which cost about $12,000 each including installation and shipping to Hawaii, with another $3,000 for the data system. Cadam's team has installed about half of those, including 60 for individual drivers, since the battery was released to the public in July. This was the first batch shipped to Hawaii.

  “;I was on Craigslist the day I arrived looking at cars and somebody was selling a plug-in Prius, an A123 converted plug-in Prius, for $44,000 complete,”; Cadam said. “;So I'm assuming it was someone who came to my shop very recently and got a car converted, and they brought it over here and are trying to make a buck off of it.”;

For this project, the U.S. Department of Energy is funding the batteries, installation and data collection through its operation of the Idaho National Laboratory. Francfort has been testing the battery since 2007 and said there have been few problems in the more than 175,000 total miles logged, especially when compared to older lead-acid batteries.

“;It's weight, space and dollar savings,”; he said. “;We try to get more energy-dense batteries. The bottom line is, whether it's you or the Air Force or any of the fleets, it's petroleum savings.”;