Any smartphone user can relate to the experience: You're at a business event, out shopping, or on an outdoor excursion when you notice that your smartphone battery has reached critical levels, and there's no way to access an outlet anytime soon. For when being disconnected isn't an option, there are plenty of emergency power boosters that can revive your cellphone until you can plug your phone back into the nearest outlet. Learn more about the latest developments in power-generating technology that won't ever show up on your utility bill.

Solar-Powered Chargers

These devices are a great way to save a little money and make sure you've always got a charge handy for your phone. Most of them are hybrid, which means they can be charged by exposure to light, or by plugging them into a USB outlet. Using a USB charge sort of defeats the purpose, but the stored energy for quick charges still comes in handy.

Even people who live in Washington State (sorry, Seattle!) can take advantage of most solar-powered chargers because many work in both natural and artificial light. The main drawback is the time it takes to collect enough energy - they need up to 20 hours to fully recharge. However, once the charger is juiced up, it typically carries enough energy to recharge a cellphone twice.

Solar-powered chargers are great for vacations and camping trips to sunny locations, for use during power outages, and as a portable backup when you're away from outlets for extended periods.

Kinetic Chargers

Physics geeks have always known about the incredible power in motion. That's why several companies have come up with ways to harness kinetic energy and transform it into battery power for phones. Kinetic chargers come in a wide range of styles, from plug-and-move devices to movement-based charging mechanisms built into the batteries themselves.

Although kinetic batteries don't really provide a reliable, long-term charge, they're great for quick power-ups when you just need a few minutes of talk time. These batteries have a finger-sized hole near the top. To charge one, you pop the battery out of the phone, stick your finger through the hole, and spin it around. Around 130 rotations will give you about three minutes to talk or fire off a few texts.

Other kinetic chargers generate greater amounts of power. Some of them are also a lot of fun, like the Watts Maker, which charges your phone while you're riding a bike. This device provides a full charge after 90 minutes of pedaling, although it does not appear to be available for purchase. Then there's the golf club hand grip charger. Shaped like the grip of a golf club, it generates electricity while you practice your swing. Again, however, this one appears to be a design idea, rather than an actual product. Even so, the idea is a marketable one. The nPower PEG is designed to recharge just by your moving around, such as by walking, running or cycling. Keep one in your purse, briefcase, backpack, or pocket, and it'll gather and store energy while you walk, jog, exercise, drive, dance, climb mountains, or even play video games.

Lung-Powered Charger

While this technology isn't quite out there for mass consumption yet, it is a pretty cool concept. The AIRE mask, created by Brazilian designer Joao Paulo Lammoglia, charges iOS devices using the power of breath.

The device itself looks like a good-guy version of Bane's breathing apparatus from "The Dark Knight Rises". It's a vent set inside molded white plastic that covers the mouth and nose, with an over-the-ears strap that encircles the back of the head. It can be used indoors or outdoors, so you could charge your iPhone or iPad while performing mundane tasks like jogging, or even sleeping. Wearing it makes you look a bit like Darth Vader, but some people will think that's pretty cool, making this one prospect with serious potential. (Into geeky stuff? Check out 6 Star Trek Technologies That Became a Reality.)

What's Next?

Despite what your power company might have you to believe, there are potential sources of energy everywhere. One technology, developed by engineers at Princeton University and currently undergoing testing, uses thin sheets of silicon rubber implanted with ceramic "nanoribbons" to convert mechanical energy into electrical energy. In plain English, it generates energy from normal human activity like walking or breathing. (Learn more about similar technologies in Nanotechnology: The Biggest Little Innovation in Tech.)

The engineers envision this material being used, for example, in shoes that could charge cell phones while walking or running. The rubber sheets also have strong potential uses for medicine. Powered by the rise and fall of a chest during breathing, they could keep pacemakers charged and negate the need to surgically replace the batteries.

If breathing can produce power, what about talking? Researchers in Korea are investigating the potential of sound energy and looking at a way to charge cell phones while you're speaking into them. These scientists have been able to convert sound into electricity using zinc oxide, the main ingredient in calamine lotion.

The need for a battery is still a major snag in mobile development because sometimes, life is just too hectic to be able to recharge your device. Chargers that work based on kinetic energy are essentially life support for dying phones, keeping things going until you can plug in again.