iPhone: The Missing Manual, 2nd Edition

Battery Life Tips

The iPhone 3G's battery life is either terrific or terrible, depending on your point of view. When accessing the 3G network, it gets longer battery life than any other phone—and yet that's only 5 hours of talk time, compared with 8 on the original iPhone.

But never mind all that; the point is that if you're not careful, the iPhone 3G's battery might not even make it through a single day without needing a recharge. So knowing how to scale back its power appetite could come in extremely handy.

The biggest wolfers of electricity on your iPhone are its screen and its wireless features. Therefore, you can get longer life from each charge by:

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

  Note

  This works because of an ambient-light sensor that's hiding behind the glass above the earpiece. Apple says that 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 the phone believes that it's in a dark room). Or by holding it up to a light as you wake it, you get full brightness. In both cases, you've saved all the taps and navigation it would have taken ...