DOUBLE DEVICES DOUBLE DEVICES Share of business travelers who regularly carry more than one: Cellphone 15% Laptop 10% PDA/other 6% Source: In-Stat SAN FRANCISCO  About 31% of business travelers lug more than one cellphone, laptop or other electronic device, says a study out Monday from researcher In-Stat. Cellphones are the most duplicated electronic: 15% of business travelers carry two or more, says the survey of 1,402 people. But a surprising number of frequent travelers — defined by In-Stat as those on the road at least 20% of the time — schlep two laptops. Duplication is common even with similar devices. One in four owners of Palm's high-end Treo cellphone said they also carry another Palm personal digital assistant. The results "surprised me," says In-Stat analyst Bill Hughes. "Multiple laptops are really heavy." The study shows that multipurpose devices are too unreliable and hard to use, Hughes says. There's still years before they reach their potential, he says. Samsung, Apple, (AAPL) Sony and others are working on it. The Treo, Apple's iPhone, Research In Motion's BlackBerry and other "smartphones" include Web access, e-mail, and other PC-like features. Sony's PlayStation Portable video game system has a Web browser and video player. That's not enough for travelers such as Troy Steward, 39. The computer systems architect from Amherst, N.Y., carries multiple electronics, including two cellphones (a Motorola (MOT) RAZR for work and Treo for personal calls). He uses his PSP only for video games, and an Apple iPod for movies and music. "I (carry) whatever it takes," he says. Why folks lug around so much stuff: •Battery life and storage. Putting a movie on the PSP would take up too much space on its storage card, Steward says. That's why he needs the iPod. About 36% of smartphone users surveyed said battery life kept them from using the phone too often, Hughes says. •Interface and synchronization. About 41% of smartphone owners said they wanted a better keyboard, while 30% wanted an expandable screen. About 35% demanded automatic synching with a PC or other electronic device. "It has to be easy" to use and update an all-in-one device, Hughes says. •Connectivity issues. Steward says having two cellphones also helps ensure that he can always get an Internet connection. Matt Holdrege, a 45-year-old telecom executive from Los Angeles, similarly uses his iPhone to connect to the Web when his laptop is offline. Holdrege, working in Kenya, also carries a second phone. The iPhone has service through cell carrier AT&T, (T) which is "very expensive" outside the USA and Europe, he says. He needs the other phone to receive calls. Conversation guidelines: USA TODAY welcomes your thoughts, stories and information related to this article. Please stay on topic and be respectful of others. Keep the conversation appropriate for interested readers across the map.