As the race to offer the first commercially viable electric car charges up, automakers hoping to cash in on environmental concerns displayed a slew of models at the Paris Motor Show on Friday.

But executives acknowledged that uncertainties linger over the batteries needed to power them: technology needs to advance to meet cost and weight requirements, and infrastructure to recharge them is lacking.

Some of the models on show are still prototypes — such as Renault SA's Z.E. Concept — while others such as Daimler AG's all-electric Smart ED, have entered the test phase.

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Most of them won't be commercially available for several years — and even then automakers say they will struggle to meet demand.

"The investments needed for electric cars are colossal," Renault CEO Carlos Ghosn said during the auto show, which opens to the public Saturday and runs for two weeks.

"The question is not whether demand will be sufficient. It is whether supply will be able to follow the demand that is already out there," he said.

Electric vehicles have been around for over a century: In 1899, the wiener-shaped "Jamais Contente" or "Never Happy" broke the 100-kilometer-per-hour (60 mph) barrier when motor cars still were a rare sight.

Hindering the development of the electric car was its capacity for energy storage: batteries lacked the performance and range required for regular use.

Since then, the technology has developed, and analysts say recent developments in lithium-ion cell technology — which Daimler, Renault, General Motors Corp. and Chrysler LLC plan to use — are promising.

Demand is being led by environmental concerns and by legislation — new EU rules are being shaped to limit carbon dioxide emissions.

GM plans to be one of the first to market with the rechargeable electric Chevrolet Volt, displayed in Paris against a backdrop of silver trees, which it says will go on sale in late 2010. GM hasn't decided yet which battery maker to use for the Volt but has already settled on the requirements: an autonomy of 40 miles (60 kilometers) and three hours to recharge.

"General Motors is betting an awful lot on the Volt, and I think its more than just an image issue, so we are all very interested in that," said Finbarr O'Neill, head of international operations for J.D. Power & Associates.

"But there are multiple answers here. It's not just electric cars. It's bringing down the cost of hybrid, further diesel growth, downsizing gasoline engines, weight reduction, stop-start technology. All of those things are going to be pushed to the limits in order to get lower emissions and greater mileage."

Chrysler last week unveiled three electric-powered models — a sports car, a four-door Jeep and a minivan — and promised to put one of them on sale in the U.S. sometime in 2010.

BMW Group is working on an electric Mini, but CEO Norbert Reithofer said he's not convinced of a breakthrough.

"There's a lot of hype about the electric cars — the numbers of electric cars available in 2020 will not be above 5 or 10 percent of the total," he said.

Daimler is working with regional electricity suppliers to build up the needed infrastructure to allow 100 electric-only versions of its Smart micro car to go in service in Berlin and Paris in the next year. From 2012, CEO Dieter Zetsche said he hopes to be producing over 10,000 per year.

Renault, which in 2005 abandoned a hybrid version of its Kangoo after customers snubbed the price tag, is being more cautious this time around, said Alice de Brauer, head of environmental strategic planning at Renault.

She said Renault failed to see a viable market for gasoline-electric hybrids and is focusing its energies on developing a fully electric car by 2012. But she said technology and infrastructure need to catch up with current requirements.

"We have a technical challenge ahead of us," she told The Associated Press. "I think we are capable."

French power provider Electricite de France SA offered a glimpse of the future with its "smart" charging terminal, currently being tested on Toyota Motor Corp.'s Prius cars in Britain. The technology is designed to recognize the car, allowing drivers to be invoiced directly no matter where they charge their vehicles.

In the meantime, carmakers sought to underscore the green achievements currently possible, with even Ferrari announcing it has cut emissions in its newest fast car, the California. Around the showroom, large numbers pasted down the sides of many models advertised the amount of carbon dioxide they emit.

Honda Motor Co. on Thursday unveiled a new five-door gasoline-electric hatchback to challenge rival Toyota's success with the hybrid Prius. Honda said its Insight would be cheaper "than any other hybrid car on the market," to make the low-emission technology affordable for more consumers. The Japanese automaker aims to sell 200,000 of the cars each year, launching next spring in Japan, Europe and North America.