The fuel cell, which the Japanese company has been developing for the last eight years, was first shown at the International Consumer Electronics Show in Las Vegas in January 2006. At that time it was about double the size of a laptop battery, but the latest version, due to be unveiled later this week at an event in Japan, is half the size, Panasonic said Monday.

The new version has a volume of 270 cubic centimeters and can deliver an average power of 10 watts with a peak output of 20 watts, Panasonic said. It weighs 320 grams.

On a 200cc charge of methanol it should be able to deliver power for 20 hours -- considerably longer than the Lithium Ion batteries used in laptop PCs today -- and when the methanol gets low all that's required is a quick refill and it's back to full capacity. This fast recharge is seen as one of the key advantages of direct methanol fuel cells (DMFCs). They are also viewed as more environmentally friendly than Lithium Ion batteries because the only by-product is a little water and carbon dioxide.

Additionally Panasonic has also developed a stand-alone DMFC charger that has a couple of USB power outlets and can be used to recharge dead gadgets such as iPods and cell phones when away from a power socket. The recharger is slightly larger at 360cc and weighs 350 grams.

Both will get their first public showing at the Hydrogen Energy Advanced Technology Exhibition 2008 that is due to open Wednesday in the western Japanese city of Fukuoka.