What can you do when your mobile-phone battery runs low and you're nowhere near a power source? New pocket-size products, compatible with most cell phones, can help. The Sidewinder ($24.95) is a hand-cranked electricity-free charger. Hook it up to your phone, and crank your way to six minutes of talk time or 30 minutes of standby time for every two minutes of turning. Or try disposable batteries, such as the Cellboost ($5.99), which plugs into your phone and provides about 60 minutes of talk time and 60 hours of standby time.