The biggest wolfers of electricity on your iPhone are its screen and its wireless
features. Therefore, you can get substantially longer life from each battery
charge by using these features:
Dim the screen. In bright light, the screen brightens (but uses more battery
power). In dim light, it darkens.
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 fi nd
the manual brightness slider in Settings.
Turn off Wi-Fi. Tap HomeÆSettingsÆWi-FiÆOn/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. Page 242 has the details.
Turn off the phone, too. In Airplane mode, you shut off both Wi-Fi and
the cellular radios, saving the most power of all.
