For years, DMFCs (direct methanol fuel cells), which typically work by mixing methanol with air and water to produce electrical power, have been promoted as an alternative to the lithium ion batteries used in notebook PCs and other portable electronics gear.
DMFCs are useful because power can be obtained instantly by inserting a fuel cartridge recharger, developers say.
Japan's mobile phone vendors spent years trying to get the battery life of third-generation mobile phones to match that of the country's second-generation digital phones.
In DoCoMo's case, the company has a prototype charger on display at Wireless Japan.
The device, which DoCoMo is developing in association with Fujitsu Laboratories, will appeal to members of the carrier's base of nearly 50 million subscribers who are looking for a quick power fix, said Kazuhiko Takeno, a manager at the company's Technical Support Group.
The recharger, which has a cradle design, is still a bit bulky at 5.9 inches by 2.2 inches by 1 inch, and it weighs 6.7 ounces.
That's because, despite being about the same size and volume as the older model (which is marginally thinner), the new prototype has enough power to recharge a mobile phone battery three times, which is much nearer to being worthwhile for customers, he said.
Fuel-cell technology is also looking viable for KDDI's customers, according to Youichi Iriuchijima, an assistant manager at the company's IT Development Division.
At last October's Ceatec Japan 2004 exhibition, Iriuchijima showed prototype rechargers from Hitachi and Toshiba, saying that improved versions would be on the market in 2006.
The Hitachi version is 4.8 inches by 3 inches by 3 inches, weighs about 6 ounces and offers two recharging options.
The Toshiba version is bigger, at 4.5 inches by 4.4 inches by 1 inch, and the prototype weighs 8.8 ounces, about twice the weight of a typical Japanese-model third-generation mobile phone.