The U.S. Army has begun using a portable fuel cell by DuPont and Smart Fuel Cell that weighs far less than conventional batteries and lasts 72 hours, the companies said Wednesday.

The M-25 cell pack and the methane fuel add up to 6.2 pounds, compared with the 25-pound regular batteries that a soldier normally would carry for the three-day mission on foot. The Army is deploying the fuel cell for testing in the field after DuPont and Smart Fuel Cell spent two years developing the product.

The M-25, which measures 3.27 inches by 2.15 inches by 9.45 inches, uses methanol as fuel and can generate 20 watts to 25 watts of electricity.

“You get more power for less weight,” said Deepak Perti, venture leader with DuPont Fuel Cells. “When soldiers are on foot on an extended mission, he has his backpack and equipment that could [sometimes weigh] about 110 pounds. When you reduce that much weight, then soldiers can carry more water, food or gear.”

Developing and commercializing portable fuel cells for the military and consumer markets has been a great challenge for fuel-cell companies. Fuel cells promise greenerstorageby running hydrogen, methanol or other fuels through a cell, where a catalyst separates the electrons from the positive ions in the fuel. A wire routes the electrons to power devices before sending them back to another part of the fuel cell for a chemical reaction that produces water or carbon dioxide or both.

But developing the right chemical process to produce electricity reliably is tricky, as many fuel cell companies have discovered. Making fuel cells small and cheap enough for portable consumer gadgets — from laptops to cell phones — remains difficult. After spending millions of dollars over the last few decades, many companies are still in research and development stages (see Fuel Cells Step Forward, Will Micro Fuel Cells Fly High, and Sweet Fuel).

The fuel cell market saw a growth of 75 percent in 2007, but that translates into 12,000 new units being shipped, according to a recent report by Fuel Cell Today. The market research firm estimated that fuel cell plants today are able to make about 100,00 units a year.

Public funding plays a key role in promoting fuel cell research. Governments worldwide spent about $1 billion on fuel cell research in 2007, said Fuel Cell Today.

Private investors are betting on fuel cells despite the technology’s limited commercial success (see Funding Roundup: Solar, Fuel Cells, Batteries Score Cash and Funding Roundup: Green Giving Keeps Going).

Fuel cell patents outnumbered patents in other cleantech fields for the first quarter of this year (see Firm Reports Decline in Cleantech Patents).

Perti referred questions about the number of M-25 in deployment to an Army representative, who didn’t return a call for comment.

Selling M-25 to the U.S. military in bulk is at least a year and half away, Perti said. DuPont isn’t focusing on developing M-25 technology for consumer market, but may do so later, he added.

DuPont is a minority stakeholder in Smart Fuel Cell.

Other companies also are working with the military to develop products.

UltraCell, based in Livermore, Calif., said Monday it has received a new funding contract to further the development of its 25-watt fuel cell, XX25. The U.S. Army Communications-Electronics Research, Development and Engineering Center Army Power Division and the Defense Advanced Research Projects Agency awarded the contract. UltraCell has engineered the XX25 to power laptops for up to eight hours using a 250 cubic-centimeter cartridge.