To fully charge your smartphone, you usually need about 30 minutes. But if you plug in your phone before you go to sleep at night, not only are you wasting energy charging a fully powered phone, you're also causing strain on the battery. Look for electric outlet adapters that have a built-in timer. These timers can be set for 30 minutes, three or six hours and then automatically cut off the power source. This lets you sleep, save energy and protect your pricey smartphone, too.