RALEIGH, N.C. - In a windowless workshop near the county landfill, a small Raleigh company has spent the past year trying to solve the nation's energy crisis one car at a time.

The cluttered Advanced Vehicle Research Center garage, tucked in an office park, can accommodate two Toyota Priuses. Lately, the bay stays full. Demand keeps the cars rolling in for a makeover some say will become standard as the car industry weans itself off gasoline. In less than four hours, the mechanics at the garage can outfit a Prius with a second battery pack. It emerges as a hybrid that can plug into a wall outlet to recharge like a cell phone.

The result: A car that breaks a once-unimaginable fuel efficiency barrier and delivers 100 miles per gallon. The spare battery costs less than 75 cents to charge and gives the plug-in Prius about a 35- mile range solely on electric power, making gasoline optional on short commutes. Retrofitting Priuses has become a full-time occupation for the Advanced Vehicle Research Center.

Even as gas prices have retreated from record highs, the cost of tanking up is changing lifestyles. Many people are driving less and ditching SUVs for smaller cars. Automakers are switching production to economy models and rushing to roll out hybrids. Research is accelerating on new technology such as long-range electric cars and hydrogen-powered vehicles.

The Advanced Vehicle Research Center is one of a handful of companies that converts the Prius or other hybrids into plug-in hybrids, doubling their gas mileage. The auto center sees demand mostly from corporate customers with fleets of cars, but recently converted its first car for a private consumer.

The center's small crew - founder and president Richard Dell, a former IBM project manager, plus two auto mechanics - can retrofit three Prius orders a day.

Toyota does not authorize or endorse these conversions, and has its own Prius plug-in in the works. But plug-in hybrids aren't expected to be available commercially until 2010 in this country. Enthusiasts aren't waiting, and with outfits such as Advanced Vehicle Research Center and other custom installers, they don't have to. Anyone who owns a Prius and can spare $10,400 can get a custom conversion.

By the end of the year, Advanced Vehicle Research Center expects to have at least 30 such plug-ins on the road.

Dell's garage is stacked with battery conversion kits, air compressors, generators and other shop equipment. On a recent afternoon, Dell, 62, sidestepped half-open cartons and scattered tools as he checked on the progress of two conversions.