Imagine you've been chatting for hours on your cell phone and it's running low on power. But instead of looking for the nearest electrical outlet, you recharge the phone with a squirt of clear liquid from a little bottle.

That's the vision of Toshiba Corp. and other Japanese electronics companies, which are readying gadgets that will swap their batteries for a long-anticipated alternative energy source: fuel cells. Fuel cells combine hydrogen with oxygen to produce electricity, providing power in a way that is potentially cleaner and cheaper than many conventional energy sources.

Long-running interest in fuel-cell technologies has accelerated recently amid soaring oil prices. Ultimately, the hope is that fuel cells will power cars or electric generators for homes. But the technology has been tricky to develop and extremely difficult to commercialize, especially because the large power systems needed for cars or generators use many parts and have been prohibitively expensive to produce.

So gadget-making companies are seeking to jump-start the technology from the other end of the size spectrum. They are developing fuel cells for small, portable devices such as cell phones or portable music players that the companies hope will be cheaper and easier to commercialize.

"We're starting with as small an application as we can and keeping costs low," said Fumio Ueno, Toshiba's fuel-cell technology chief. "We think it's better to start that way and grow into larger applications."

Unlike batteries, fuel cells generate electricity rather than just store it. They don't contain the environmentally hazardous metals or chemicals that most batteries do. In fact, fuel cells in theory don't pollute at all: They combine hydrogen with oxygen from the air to produce electricity, with only water as exhaust.

In practice, obtaining hydrogen using clean energy sources such as solar power is still too expensive, so for now most companies are experimenting with ways of getting hydrogen from natural gas. Many of those processes produce carbon dioxide, the main suspect among global-warming gases, and so aren't completely eco-friendly.

Toshiba and others are developing fuel cells that run on methanol, an alcohol also derived from natural gas. Toshiba's most basic version of the fuel cell is about the size of a cigarette lighter and, like old-style lighters, can be refilled from a bottle when empty. That means users can juice up portable gadgets while on the run, rather than plugging into a wall socket to recharge. This feature could grow in importance as cell phones and other devices start to do more things -- such as playing music or video clips -- and drain more power.

Toshiba also claims the fuel cells it has developed will let users talk on a cell phone for about five hours -- 21/2 times longer than the lithium-ion batteries commonly used in cell phones now. Toshiba's first fuel-cell cell phones, however, probably will be hybrids that combine regular batteries with fuel cells to increase reliability in the early stages of the technology.

Toshiba and Hitachi Ltd. separately are developing cell phones that run on or are recharged by fuel cells for Japanese mobile carrier KDDI Corp. Fujitsu Ltd. is making a similar type of cell phone for NTT DoCoMo Inc.

All of the companies are hoping to roll out the first devices around 2007, by which time they expect regulations allowing methanol on airplanes -- a near-necessity for sales to many customers -- will have been finalized.

Indeed, although companies such as South Korea's Samsung Electronics Co. -- and Hewlett-Packard Co. and Motorola Inc. in the United States -- are also experimenting with small fuel cells, most of the gadget manufacturers readying fuel-cell products are based in Japan.

Big U.S. device makers are more likely to research the technology to make sure they can integrate it into their products and will leave much of the fuel-cell manufacturing to others, said Jerry Hallmark, who leads Motorola's energy-technology group.

Smaller ventures may be squeezed by the high costs of commercialization. "There are a lot of people developing fuel cells right now that will run out of money before they get products out," Hallmark said.

Motorola, while researching ways of powering cell phones with fuel cells and hoping some of its technology will be used in final products, hasn't decided whether it will make fuel cells.