PARIS - 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.

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.