Lead-acid batteries. That's a four-letter word for many in the emerging plug-in hybrid and electric vehicle industry, where advanced battery chemistries like lithium-ion and nickel-metal-hydride have taken the front seat.

But advanced lead-acid battery maker Axion Power International Inc. says that its new carbon electrode technology can give the world's oldest battery chemistry a new lease on life for vehicles known as "micro" or "mild" hybrids – and it has a deal with big battery maker Exide Technologies to put the proposition to the test.

New Castle, Pa.-based Axion uses a carbon electrode to give the battery a lifespan three to four times longer than those using traditional lead negative electrodes, CEO Tom Granville said.

That technology comes from a Russian company that had been developing it for superconductors, and Axion has invested about $50 million in adopting it for use in batteries since its 2003 founding, he said.

The beauty of Axion's approach, Granville said, is that it can be put in place of existing vehicle lead-acid battery lines.

"When that cover gets sealed, you can't tell the difference between our battery and the standard old lead-acid car battery," he said – except that Axion's batteries weigh about half as much without all that heavy lead in them.

Similar arguments have been made by other companies developing various forms of advanced lead-acid batteries, such as Firefly Energy, Atraverda, Johnson Controls, Effpower and Applied Intellectual Capital (see High-Tech Lead Acid Batteries for China's Electric Scooters).

Axion can make about one million batteries per year at the defunct battery plant in New Castle that it bought in 2006, Granville said. But a supply partnership with Exide, one of the world's largest car battery makers, that it announced in April could expand that significantly, he said.

Granville wouldn't provide volume figures on the four-year supply agreement. But he did say that Axion was seeking a $52 million stimulus grant from the Department of Energy to help it boost production at its factory at the same time it works with Exide.

Beyond improving on existing car batteries, Axion's PbC (lead carbon) technology could be suitable for what Granville called the "stop-start" hybrid market, and what Axion CTO Edward Buiel called the "micro" "or "mild" hybrid market.

Those last two terms refer to hybrid vehicles that use their electric motors primarily or solely for things other than powering the drive train.

Mild hybrids that supplement an internal combustion engine's torque to drive the car forward include Honda's Civic and Accord hybrids.

Micro hybrids, which don't supply any torque at all from the electric motor, include the GM Silverado hybrid and a host of upcoming vehicles promised by companies including Peugeot-Citroen, Daimler, and Ford Motor Co. in Europe.

Both types of hybrids can be considered "stop-start" hybrids, in that they can shut down their engines completely when at stop signs or traffic lights. That can cut fuel use by about 10 percent to 15 percent, Granville said.

Mercedes-Benz has said it wants to equip a wide range of its cars with such "stop-start" engines by 2011, according to a May report from Autocar.

Lead-acid batteries still don't have the same energy density as lithium-ion batteries – meaning they can't hold as much energy by weight – making them a "struggle" for including in fully electric vehicles, he said.

But lead-acid batteries do have good power density, making them good at capturing power from regenerative braking systems, he noted.

Axion's partnership with Exide isn't limited to vehicles – the two are also developing batteries to store power on the electricity grid or at other stationary sites, Granville said.

Axion could supply suchstoragesystems for about $250 to $280 per kilowatt-hour, compared to costs of $1,000 and up that are generally cited for competing lithium-ion storage solutions, he said.

The company has a deal with the New York State Research and Development Authority to test its batteries for grid storage and to store energy from a solar power system at CUNY College in New York City. It's also working with San Diego-based Envision Solar on its plans for solar-powered car charging stations.