DETROIT -- One reason electric and plug-in hybrid vehicles have hit the market with a thud is that there are strings attached. Models such as the Chevrolet Volt and Nissan Leaf are tethered.
Drivers need to plug in to recharge the battery.
A number of companies are developing ways to cut the cord, to replenish the battery wirelessly with a mat that sits on the floor.
Coils on the underside of the car engage the charger when the car is parked over them.
The mats are plugged in while the car isn't. Automakers and suppliers expect to have the chargers ready for sale around 2015.
"The feedback we see from initial Volt and Leaf buyers is that, 'Gee, these cords get really dirty; gee, these cords get all tangled; what a pain in the neck,'" said Phil Gott, an IHS Automotive analyst specializing in powertrain research. "A wireless charger truly gives you total freedom."
Automakers are looking to such vehicles to comply with regulatory pressure to boost mileage and pare emissions.
However, electric and plug-in vehicles aren't even considered by 96 percent of consumers globally, Deloitte LLP said in a survey last year.
Price and driving range deter purchases, Deloitte said, and so does charging time, which ranges from three to more than eight hours.
Tesla Motors Inc., the electric-car maker that delivered its first wholly company-produced sedans last week, had said it's close to announcing a plugged-in "supercharger" network that can re-power one of its cars in less than an hour.
Nissan Motor Co., Delphi Automotive Plc, Volkswagen AG's Audi, Toyota Motor Corp., Mitsubishi Motors Corp., Qualcomm Inc., Evatran LLC, and Brose Fahrzeugteile GmbH & Co. are among the companies developing wireless chargers.
General Motors, the largest U.S. automaker and maker of the Chevrolet Volt, invested $5 million in a private company called Powermat and was joined by Procter & Gamble Co. and Jay-Z last year.
So far, GM says it's only using the technology to charge smartphones and other devices in the car.
The chargers work one of two ways: by induction, similar to the way the battery on an electric toothbrush charges when it's set back on its base, or magnetic resonance.
Delphi's charger, using a technology developed by WiTricity Corp., uses a magnetic field to transfer the charge between coils in the mat, about the size of a laptop, and bolted onto the underside of the car.
The gap can be as wide as 10 inches (25 centimeters), depending on the car's clearance, said Randy Sumner, Delphi's director of hybrid electric vehicle business and technology development.
The charger, using technology developed at the Massachusetts Institute of Technology, can send 3 kilowatts of electricity quickly enough to recharge a battery in about four hours, Sumner said.
Two coils are tuned to resonate at the same frequency, creating the connection. Audi, Toyota and Mitsubishi also are working with WiTricity.
Magnetic resonance allows more margin for error than inductive charging, Sumner said. Inductive chargers require more precise alignment for recharging.
Magnetic resonance allows for a lateral, or left-to-right, range of plus or minus 10 centimeters, he said.
The chargers probably will sell for more than $2,000, at least twice the price of current charging stations, Sumner said.
They are also less efficient. About 10 percent of power is lost in transmission, and the goal is to cut that by half, Sumner said. Kinks are still being worked out.
A charging mat is flat and warm, so how to keep a family cat from napping on one? How does a user keep metal away?
A group of engineers from suppliers and automakers has been meeting for a year to resolve such issues and to develop standards to make all chargers work on all cars, Sumner said.
The other hurdle is the market. GM sold 7,671 plug-in hybrid Volts and Nissan 9,674 all-electric power Leafs last year, according to researcher Autodata Corp.
Through May, Volt and Leaf combined deliveries totaled 9,670. Nissan sold 510 Leafs in May, a 55 percent slide from a year earlier. The Volt has a starting price of $39,145 while Leaf's is $35,200 before tax credits.
Electric versions of gasoline- powered models also cost more. Toyota said in May said its electric RAV4 sport-utility vehicle, to be sold in California, will cost $49,800, more than twice the gasoline version.
Tesla supplies the electric RAV4's batteries and motor. Pike Research, based in Boulder, Colorado, forecasts sales of 359,000 plug-in and all-electric vehicles in the United States by 2017.
AutoPacific Inc., an industry researcher in Tustin, Calif., estimates that plug-in and electric car sales will total 320,000 units in 2017.
Offerings of rechargeable vehicles are expanding. Toyota last year introduced a plug-in version of its Prius hybrid car.
Ford Motor Co. began selling an electric Focus this year and a plug-in version of the Fusion goes on sale next year.
Delphi Chief Executive Officer Rodney O'Neal said consumer demand hasn't caught up with technology.
"There are a lot of things that are possible," he said. "The questions is, can you do it cost effectively and does the world care, and can you make money and create value for your shareholders?"
Wireless public chargers may mitigate concern that drivers will run out of electricity before they can get home to recharge.
The number of public charging stations globally is projected to more than triple this year to 98,503 from 28,479 in 2011, according to an April 27 Bloomberg New Energy Finance report.
Most of the new stations will be in China and Europe, according to the report.
A test under way in London is looking at how to embed wireless charging mats in city streets and parking garages, said Andrew Gilbert, Qualcomm executive vice president.
The company wants to license the technology to automakers and charger manufacturers.
Qualcomm is outfitting as many as 50 electric vehicles with chargers, he said.
"Plug-in is not a bad solution; we just see this as a great opportunity to really improve the experience," Gilbert said. "The power source is the same; it's just whether it goes over the air or a cable."