Mercedes-Benz is poised to be the first automaker to market a hybrid vehicle with lithium ion batteries when it launches a mild hybrid version of the S-class sedan in 2009. The vehicle is expected in the United States in 2009.

Toyota Motor Corp. had planned to equip the next-generation Prius and its other hybrids with the powerful high-tech batteries but now says its batteries won't be ready until 2010 or 2011.

Toyota also is testing a car in Japan that uses lithium ion batteries for a stop-start system, but the car, called the Vitz, is not a hybrid.

At the Frankfurt motor show today, Mercedes executives said the 2009 S 400 will have a mild hybrid powertrain with an electric motor that also acts as a starter-generator.

A Mercedes executive in Frankfurt said the batteries will be supplied by Johnson Controls-Saft, a joint venture formed last year by the U.S. interior supplier and the French battery maker.

Johnson Controls-Saft expects to complete a new plant to manufacture lithium ion batteries for its European customers this year. The plant is in Nersac, France.

Although the battery pack in the S 400 won't be under as much strain as batteries in a full hybrid or a plug-in, Johnson Controls-Saft CEO Mary Ann Wright said engineers still submitted the batteries to the same rigorous testing as those that will be used in full hybrids.

"We're confident in our design and approach to safety management," said Wright, who oversees the engineers who are designing and developing the batteries.

Wright said the batteries are designed to last the life of the vehicle.

Mercedes says the S 400 hybrid can accelerate from 0 to 60 mph in about 7.3 seconds. Mercedes also claims that the S 400 will be the most fuel-efficient luxury sedan in the world.

Lithium ion batteries are expected to replace nickel-metal hydride batteries used in today's hybrids. But lithium ion batteries can overheat and catch fire.

Says Wright: "We are very excited to be part of this project with Daimler. We have been working hard together to develop an excellent hybrid system."

You may e-mail Richard Truett at rtruett@crain.com