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 you to find the manual brightness slider in Settings (Brightness).

• Turning off 3G. If you don't see a icon on your iPhone 3G's status bar, then you're not in a 3G hot spot (Screen Icons), and you're not getting any benefit from the phone's battery-hungry 3G radio. By turning it off, you'll double the length of your iPhone 3G's battery power, from 5 hours of talk time to 10.

  To do so, from the Home screen, tap Settings → General → Network → Enable 3G Off. Yes, this is sort of a hassle, but if you're anticipating a long day and you can't risk the battery dying halfway through, it might be worth doing. After all, most 3G phones don't even let you turn off their 3G circuitry.

• Turning off Wi-Fi. From the Home screen, tap Settings→Wi-Fi→On/Off. If you're not in a wireless hot spot anyway, you may as well stop the thing from using its radio. Or, at the very least, tell the iPhone to stop searching for Wi-Fi networks it can connect to. Fetch New Data has the details.

• Turning off the phone, too. In Airplane mode, you shut off both Wi-Fi and the cellular radios, saving the most power of all. Airplane Mode and Wi-Fi Off Mode has details.

• Turning off Bluetooth. If you're not using a Bluetooth headset, then for heaven's sake shut down that Bluetooth radio. In Settings, tap General, and turn off Bluetooth.

• Turning off GPS. If you won't be needing the iPhone to track your location, save it the power required to operate the GPS chip and the other location circuits. In Settings, tap General, and turn off Location Services.

• Turning off "push" data. If your email, calendar, and address book are kept constantly synced with your Macs or PCs, then you've probably gotten yourself involved with Yahoo Mail, Microsoft Exchange (Chapter 15), or MobileMe (Chapter 14). It's pretty amazing to know that your iPhone is constantly kept current with the mothership—but all that continual sniffing of the airwaves, looking for updates, costs you battery power. If you can do without the immediacy, visit Settings→Fetch New Data; consider turning off Push and letting your iPhone check for new information, say, every 15, 30, or 60 minutes.

Finally, beware of 3-D games and other add-on programs (Chapter 11), which can be serious power hogs. And turn off EQ when playing your music (Familiar iPod Features).