Samsung claims that it has developed a fuel cell for laptops that lasts almost twice as long as existing models. The world's largest maker of plasma display panels said yesterday that the new portable fuel cell has an energy density of 200 watt hours per liter, the highest among fuel cells currently on the market.

Fuel cells for laptops from Japan's Toshiba and NEC average 100 to 130 watt hours per liter in energy density.

Energy density refers to the amount of wattage produced per hour. The higher the energy density, the longer-lasting the fuel cell.

Fuel cells are powered by liquid methanol, and the new Samsung cells contain around 200 cubic centimeters (12 cubic inches) of the chemical fuel, or about enough to fill a small milk carton. Samsung's fuel cells, which go into mass production in 2007, can power a laptop for up to 15 hours.

At 23 centimeters wide, 8.2 centimeters long, and 5.3 centimeters high, the product weighs less than 1 kilogram, making it more compact than its rivals.

A team of 40 researchers and a budget of around 10 billion won ($9.5 million) has gone into the development of the fuel cell.

Fuel cells have several advantages over rechargeable batteries; not only do they last longer, but they can also be recharged almost instantly and contain no toxic chemicals.