BOULDER - Murphy's Law exists in the wireless world.

Batteries in cell phones and personal digital assistants die at the worst possible moment. Parents lose contact with peripatetic offspring in the midst of a crucial conversation. Teens suddenly can't text message friends about plans for pizza and a movie.

What users of mobile devices need, said Gil Karpel, is "a quick, convenient emergency charge." To meet that need, he and his wife, Shelley, co-founded Boulder-based Cell Charge Colorado Inc. in 2007.

The firm, which currently focuses on the Denver metropolitan region, places phone-charging kiosks in high-traffic locations where consumers are likely to be willing to linger for the 20 or so minutes it takes to recharge a battery.

Ideal sites offer a place for people to sit, eat and chat while batteries recharge. Current sites include food courts at area malls and the Alferd Packer Grill in the University Memorial Center on the University of Colorado at Boulder campus.

Each kiosk can simultaneously charge as many as 18 cell phones, personal digital assistants and digital audio players. The kiosk also disinfects and sterilizes the devices.

Still, the number of batteries recharged isn't the crucial business metric. In fact, at some kiosks, recharging a battery is free.

The kiosks are used as advertising vehicles.

For every person who stops to recharge a phone at a given location, Gil said, "A couple of hundred others have checked out the kiosk," which exposes them to a continuous loop of advertisements displayed on a 17-inch liquid crystal display monitor.

"It's a new concept in out-of-home advertising," Gil said. "It's not like standard print or television."

Advertisers on the 11 Cell Charge kiosks currently deployed in the Boulder-Denver area include wireless carrier Cricket Communications Inc., the Bernardi Real Estate Group, Flatirons Subaru and Nissi's, a restaurant and music performance venue in Lafayette. The cycle also includes public service announcements for Mile High United Way and the Make-a-Wish Foundation.

Segments are typically 10 to 30 seconds long and can be static displays or videos.

"You don't want to have too many advertisements," Gil said. "You want the entire loop to show during a single recharge cycle. There's nothing else like this. Eventually these kiosks will be as commonplace as automated teller machines."

Cell Charge "places" kiosks in lieu of selling them. It is responsible for routine maintenance such as checking periodically to see that phone leads are intact. "Kids like to play with the leads," Gil said.

The standard 24-month contract template posted on the firm's Web site indicates that kiosk locations keep a percentage of the revenues earned the battery-charging service. Revenues from the kiosk at Boulder Community Foothills Hospital support the volunteer program there.

The kiosk's underlying technology, developed in China, came to the U.S. in 2007 after deployments throughout Asia, Europe and Canada.

The market potential here is large and growing.

According to a study released earlier this year by the Pew Internet Project, 62 percent of American adults use cell phones or personal digital assistants in nonvoice activities - such as sending text or e-mail messages, taking pictures or looking for maps - while away from their homes and offices. Among the 18- to 29-year-old population that advertisers covet, the figure is 73 percent.

Browsing the Web, listening to music and checking e-mail all consume battery power. Depending in part on the kind of battery and the volume and type of use, a battery might last just an hour.

In conducting due diligence on the kiosk business, Gil and Shelly trusted the evidence of their own eyes. While visiting Tulsa, Okla., the home of Take Charge Media LLC, the national distributor for the kiosks, they saw people in food court malls huddling over the charging stations with slices of pizza in hand.

They decided to get in early rather than risk missing the opportunity. Gil estimated a potential for 100 to 200 kiosks in the Denver metropolitan area. Cell Charge Colorado has surpassed the 10 installations he believes necessary to establish credibility with advertisers. The firm also has distribution rights for the rest of the state.

Describing advertising spending in the current economy as a wild card, Karpel said Cell Charge Colorado "will not do too much too quickly."

Smart phones, which combine the capabilities of cellular phones and personal digital assistants, are gaining popularity. Canalys.com Ltd., a United Kingdom-based consulting firm, said shipments of smart phones and wireless handheld devices in North America reached 20.9 million in 2007, up from 10.3 million in 2006.

That spells opportunity for Cell Charge.

"New smart phones use lots of energy," Gil said. "Batteries can't keep up."