In an interview with The Asahi Shimbun, Masao Nakamura said NTT is jointly developing the methanol-fueled cellphones with Fujitsu Ltd.

Nakamura said that when used with existing batteries, the fuel-cell devices will expand phone operation time to four times the current standard.

New services such as "one seg," which is used to view digital TV broadcasts on mobile devices such as cellphones and car navigation systems, quickly drain conventional cellphones of battery power.

Methanol will be used in the fuel cells, which will be attached externally to the cellphone. A prototype fuel cell was developed last year. It is 15 centimeters long and 5.6 cm wide. The 1.9-cm thick cell weighs 190 grams.

With an 18-milliliter cartridge of methanol inserted, the fuel cell lasts about three times longer than the lithium-ion battery used in NTT DoCoMo's third-generation FOMA cellphone.

NTT DoCoMo and KDDI Corp.'s au service both began offering one-seg compatible cellphones last year. Demand has been rising, but consumers say the lack of long battery operating time is a drawback.

Current battery capacities only provide three to four hours of TV viewing on the phones.

Phone service providers are also offering fixed billing rates for packet-data sending, which lowers the cost of using such data-intensive functions as digital TV on mobile devices.

"We don't foresee much dramatic increase in capacities for lithium-ion batteries. By carrying along a fuel cell and replaceable fuel cartridges, one will be able to use a cellphone (to view TV) even in places where recharging is not possible," Nakamura said.

KDDI is developing an internal fuel cell for cellphones, but the company has not yet announced when the product will be on the market.