It may be years before your car is powered by a fuel cell, but your handheld computer won't have to wait too long if engineers at MTI MicroFuel Cells have their way.

To bring this eventuality closer still, MTI Micro has unveiled the latest prototype of its direct methanol fuel cell, a power supply that is about the size of a deck of playing cards and promises to let handheld computers, mobiles and other small computing devices work away from a power outlet for about 10 times as long as they can today, according to MTI Micro chief executive officer Bill Acker.

Due for commercial release in 2004, the portable power supply has been designed to replace an electrical outlet for recharging mobile phones and handheld computers. That's because the latest prototype of MTI Micro's fuel cell only generates power. To actually deliver juice to a device, the fuel cell pack requires a companion battery.

"In order to go to market, the initial entry point will be an auxiliary accessory device," Acker said.

The company is working with device manufacturers to create versions of the power supply that can be plugged into a device to recharge a current lithium-ion battery or act as an alternative power source. It hasn't yet announced any specific partnerships, though company officials demonstrated the latest prototype working with a converged phone-PDA (personal digital assistant) from Samsung.

Future versions of MTI Micro's technology will be combined with a small battery to allow the pack to be contained within the device to replace the lithium-ion battery.

The power supply makes energy out of methanol fuel. When it runs out of power, all a user has to do is insert a new fuel cartridge which is about the same size as the ink cartridge in a fountain pen.

MTI Micro is not alone in its pursuit of making fuel cell technology a mainstream source of power for portable devices. Casio has developed a fuel cell power pack for a laptop computer that will be about the size of a large conventional laptop battery when it is ready for commercialisation in the next two years.

MTI Micro is designing its fuel cell system to be easy to manufacture so it can be made cheaply enough for the mass market, Acker said. The company doesn't yet have a target price for its product, but he said it should be competitive with current lithium-ion batteries.