iPhone: The Missing Manual, 3rd Edition

Battery Life Tips

The battery life of the iPhone 3G and 3GS is either terrific or terrible, depending on your point of view.

If you were an optimist, you'd point out that when these phones are using AT&T's 3G network, they get longer battery life than any other 3G phone. You'd also extol the 3GS's even better battery, which goes about 20 percent longer than the 3G's.

If you were a pessimist, you'd observe that the 3G and 3GS get only 5 hours of talk time, compared with 8 hours on the original iPhone. And that if you're not careful, you might not even make it through a single day without needing a recharge.

So knowing how to scale back your iPhone's power appetite could come in extremely handy.

The biggest wolfers of electricity on your iPhone are its screen and its wireless features. Therefore, these ideas will help you squeeze more life out of each charge:

• Dim the screen. In bright light, the screen brightens (but uses more battery power). In dim light, it darkens.

  Note

  This works because of the ambient-light sensor that's hiding behind the glass above the earpiece. Apple says it tried having the light sensor active all the time, but it was weird to have the screen constantly dimming and brightening as you used it. So the sensor now samples the ambient light and adjusts the brightness only once—when you unlock the phone after waking it.

  You can use this information to your advantage. By covering up the sensor as you unlock the phone, you force it into a low-power, dim-screen setting (because ...