All-electric cars no magic bullet: scientist

That may not be a bad thing, as it will persuade consumers to choose the best blend of electric- and gas-powered hybrid vehicle to suit the type of driving they do.

"Ideally, everybody wants an electric vehicle. Realistically, from a cost point of view, what is the solution that allows you to go mass market? How can the customers save money?" said Aymeric Rousseau, who analyses such problems at Argonne National Laboratory, a government-funded research center hosting a conference on lithium battery technology.

Rousseau is working with the U.S. Environmental Protection Agency to offer realistic appraisals of the likely range of the next generation of plug-in electric vehicles like General Motors' Volt.

Rousseau previously helped the agency lop 10 percent or more off of promised miles-per-gallon estimates on existing gas-powered vehicles, which were posted on 2008 models.

The goal is to promise drivers of a lithium-ion battery equipped electric hybrid vehicle a 40-mile range on one charge, but that may be a gross exaggeration, he said.

Aggressive driving - faster acceleration and driving at faster speeds - may cut that range to between 28 and 32 miles. Using the air conditioning may reduce the vehicle's range to around 15 to 20 miles, he said.

In response, the vehicle's gas-powered engine will kick in two or three times during an excursion, which actually is a cost-effective response and will help extend the life of the battery, Rousseau explained.

People who drive on city streets and need travel only a few miles can use battery-only power. Those who have a longer commute at high speeds - or who drive aggressively with the air conditioning on - may want a smaller battery to improve the vehicle's overall efficiency, Rousseau said.

For different types of trips, renting a different type of hybrid vehicle may be most efficient, he said.

Another Argonne researcher told the conference a highly efficient diesel engine was much more cost-effective for highway driving than a hybrid vehicle with a lithium battery, based on the current cost of fuel and electricity. But the hybrid would beat the diesel vehicle in city driving.

Another variable to consider is the cost of making batteries.

With nickel hydride batteries now in vogue in such hybrids as Toyota's Prius, nickel prices have risen sharply. That has made lithium-ion batteries, which are a more promising technology because they can hold more power in a more compact space and have other advantages, more enticing as an alternative. Of course, lithium is likely to rise in price if it is used for vehicle batteries as well as laptop batteries, Rousseau said.

"There is no single silver bullet," he said on the sidelines of the conference. "There is not one technology that will be best for everybody. Our goal is to understand how people drive, and depending on how they drive, what is the impact of one technology or another, from a fuel efficiency point of view, and a cost point of view."