Got yourself a solar battery charger? No? You've got problems.

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Uh oh. That shortcut you took through the woods has led you into a maze. You're lost, and somehow you've ended up off the main road with no way back in sight -- and your car ­is running low on gas. To make matters worse, you've told no one where you're going and your phone is running out of juice. The measured beeps it issues to alert you of its imminent demise seem like a reminder of your own as well.

Luckily for you, there's a break in the forest canopy. You see a wide meadow full of sunshine streaming down into the tall grass up ahead. You park your car and walk to the meadow. Once clear of the trees, you look up, and there's not a cloud in the sky. Yes, you're going to be just fine. After rummaging around in your glove compartment for a bit, you retrieve your solar-powered battery charger. You plug the USB cable from the charger into your cell phone, flip the charger over so that its small solar panel faces skyward, find your cell phone signal, place the whole setup on a stump, kick back and wait. This is a probably a good time to relax and read a book, since you know that help is on the way.

­Before the first decade of the 21st century, you would have been out of luck had you found yourself in a scenario like this one. Lately, however, a number of companies have created a spate of battery chargers that use the power of the sun to fuel everything from cars to gadgets to AA batteries. Find out about the mechanics behind solar battery chargers on the next page.

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