Travelin’ light is the only way to fly.

With every new iPod and iPhone model, Apple boasts longer battery life—but sometimes, that just isn’t enough. If you’re worried about running out of juice on a long trip, the Oliver XP600 can keep your gadget running a little while longer.

How much longer depends on the gadget and what you’re using it for—we tested it with an iPhone 3G (in Airplane mode with full screen brightness and half volume) when watching movies, a battery-intensive task. Without the XP600, the iPhone played 4 hours, 55 minutes of continuous video. Then, we recharged the iPhone, fired up the movie again, and attached the XP600 when the iPhone gave us the “20% battery remaining” warning. Instead of playing 25 minutes and dying, the iPhone-with-Oliver played another 60 minutes, for a total time of 5 hours, 30 minutes, or 12 percent longer. Not earth-shattering performance, but good enough for another few episodes of Seinfeld on your cross-country flight.

But we hope you’re bringing a laptop too, because once the XP600 croaks, you need to recharge it via USB, since it doesn’t come with an AC adapter. (XPAL says it plans to offer one at some point.) If you want to travel light, pick up one of Apple’s USB Power Adapters ($29, www.apple.com)—the tiny adapter, which comes with the iPhone 3G, will charge the XP600 with 5 volts, the same as a USB port on your Mac.

The XP600 is credit card sized and only 1/4 inch thick, making it darn-near wallet sized (especially if you have a honkin’ George Constanza wallet). It comes in a black velvety pouch with a cable attachment and a collection of seven tips, for iPod/iPhone, plus BlackBerry, LG, Motorola, Nokia, Samsung, and Sony phones. If you ever need more tips, just register your XP600 with XPAL, then log in to www.freetipsforlife.com or call 866-XPALPOWER, and they’ll send you two “free” tips every year (you pay $3.95 for shipping).