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NEW YORK -- Anyone who relies on a rechargeable-battery-powered personal digital assistant knows the frustration of watching it drain when no AC outlet is near to juice the device. Electric Fuel feels your pain. The company released its lightweight, inexpensive PDA Instant Power Charger here at PC Expo (part of TechX NY) this week.

The PDA Instant Power Charger sells for $20. The package includes a special adapter that connects to your PDA and one disposable PowerCartridge. Additional cartridges cost $10. Electric Fuel offers adapters for most (but not all) Handspring, Palm, and Windows CE based handheld models.

The cartridge weighs less than 3 ounces, and is about 2 inches long by 2 inches wide and about 0.5 inch thick. It uses a battery technology called zinc air chemistry, which has been around since 1894, says Jonathan Whartman, vice president at Electric Fuel. Such batteries draw oxygen from the air to operate. The technology is widely used for hearing aids, Whartman says. It's good for that application because the batteries use low-voltage currents of electricity. Electric Fuel makes batteries for electric vehicles as well as hearing aids, Whartman says.

For the Instant Power Charger, Electric Fuel tweaked the technology significantly to create the higher voltages needed to recharge larger items, Whartman says. To draw the necessary oxygen, the cartridges have a distinct, perforated surface.

The company also markets the Instant Power Charger for cell phones, a product that PCWorld.com reviewed favorably.

Three Charges on the Fly

You can use your PDA while it recharges. Each tiny charger should be good for charging a PDA to about 80 percent capacity three times, Whartman says. Your actual mileage may vary depending on the type of PDA, and whether you're using it during the charge. The adapter that connects the charger to the PDA has a built-in timer that halts charging after two hours, but you can easily reset the adapter for two more hours to ensure a full charge, Whartman says.

To increase the PowerCartridge's shelf life, Electric Fuel includes an airtight bag for storing it between charges. The cartridge will eventually dry up if left exposed to the air, he says. Resealed cartridges last up to three months (you dispose of them as you would a used alkaline battery); an unopened and sealed cartridge has a shelf life of about 36 months, he says.

The increasing popularity of PDAs portends a receptive market for Electric Fuel's charger, Whartman says. And while PDAs are becoming more power hungry than ever before, the battery technology that fuels those units isn't evolving quickly enough, he says.

After all, he says, no matter how powerful the PDA, "You're only as good as your battery."

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