A U.S. company says its portable, pocket-size fuel cells can charge a smartphone a dozen times before they need refilling with butane. Lilliputian Systems, based in Massachusetts, said it had signed an agreement with retailer Brookstone to carry its portable USB power source, which will be sold under Brookstone\'s brand. The fuel cell is about the size of a thick smartphone while the lighter fluid-filled refill cartridges are about the same size as a cigarette lighter, CNET.com reported Tuesday. The fuel cell can charge any device that has a USB cable, its maker said. Lilliputian Systems is the first company to deposit a solid oxide fuel cell membrane onto a silicon wafer, Mouli Ramani, vice president of business development, said. Lilliputian expects the idea of portable power will be attractive to travelers, college students and even teenagers who spend a lot of time with mobile devices. \"Anyone who wants to be liberated from sticking a phone into a wall outlet,\" Ramani said. The fuel cell will be able to fully charge an iPhone 4 between 10 and 14 times with one cartridge, Ramani said, which could mean two weeks of use for an average user.