US researchers have demonstrated a prototype miniature fuel cell which they claim could soon replace rechargeable batteries in cell phones, PDAs, laptops and other portable devices.

The team from the Lawrence Livermore National Laboratory (LLNL) explained that fuel cells are electrochemical energy conversion devices that convert hydrogen and oxygen into electricity and heat.

Like a battery, a fuel cell can be recharged while power is being drawn from it but, instead of recharging using electricity, a fuel cell uses hydrogen and oxygen.

LLNL's Jeff Morse said that the fuel cell could be cheaper, smaller and contain more energy than any battery or alternative fuel cell technology.

"The higher energy capacity of such a product will lead to further new classes of personal electronics, such as autonomous sensors and communication devices that are not currently possible with existing battery technologies," he said.

LLNL's patented method for making thin-film fuel cells combines microcircuit processes, micro-fluidic components and micro-electrical-mechanical systems (MEMS) technology to provide a lighter, longer-lasting power source.

Morse maintained that the MEMS-based fuel cell power source will replace rechargeable batteries, such as lithium-ion and lithium-ion polymer, in cell phones, laptops and handheld devices.

"The MEMS-based fuel cell has been designed to compete with existing rechargeable batteries in the respective marketplaces," he said.

LLNL predicted that the fuel cells could cut the use of batteries by 50 per cent, with total savings of more than $2bn per year.

In similar developments, NEC and two Japanese government affiliated research institutes announced the development of a fuel cell for use in mobile devices which makes use of carbon nanotubes.

NEC expects to commercialise the technology sometime between 2003 and 2005.

Motorola, meanwhile, has developed a tiny fuel cell that is being developed with Los Alamos National Laboratory that converts the low voltage of a fuel cell to the higher voltage needed to power electronic devices.