Hyundai wouldn't say how many fuel-cell Tucsons it expects to lease. The company believes that fuel cells will power the next generation of cars, appealing to affluent, environmentally conscious customers because affordable battery technology has not advanced enough."This is the sort of technology that makes batteries look old-fashioned," says North American CEO John Krafcik. But skeptics say hydrogen fueling stations are more expensive than electric car charging stations, partly because electricity is almost everywhere and new and safe ways for producing, storing and transferring hydrogen will be needed. Carlos Ghosn, chief executive of Nissan Motor Co., which has bet heavily on electric vehicles for its future, is one vocal skeptic. "Having a prototype is easy. The challenge is mass-marketing," he told reporters. He said he did not see a mass-market fuel cell as viable before 2020. __ Justin Pritchard contributed from Los Angeles. Kageyama reported from Tokyo.