Q: I just got a new iPhone 3GS and I want to watch movies on an 8-hour plane trip. Any suggestions? Battery life is much less than my old iPhone.
A: For using your iPhone to watch movies during a long plane trip, the simplest thing to do is ensure that it is in “Airplane Mode” and to keep the screen brightness adjusted as low as possible. The major sources of power consumption on the iPhone are the cellular, Bluetooth and Wi-Fi radios and the display backlight. We performed some battery tests in our iPhone 3GS Review which indicated that you should be able to easily get between 7 and 8 hours of battery life even with the cellular and Wi-Fi radios turned on and your screen brightness at 50% and volume level at 50%. Our tests following Apple’s methodology of enabling call forwarding and turning “Ask to join Wi-Fi Networks” off saw an increase in battery life to 10 hours, since the Wi-Fi and cellular radios are more dormant in this mode. In Airplane Mode you should easily get 10 hours of video playback.
That having been said, getting off the plane with an iPhone that’s nearly drained of power is not likely going to be very useful. If you plan to travel with your iPhone, we would strongly recommend picking up an external iPhone battery pack such as the FastMac TruePower IV Universal Battery Charger (iLounge rating: B+), Just Mobile Gum Pro Portable USB Power Pack (iLounge rating: A-) or Mophie Juice Pack Air (iLounge rating: B). Each of these has a slightly different form factor and price, but generally if you’re looking for maximum charging power, the TruePower IV at 3300 mAh and Gum Pro at 4400 mAh are the best we’ve seen, easily providing 3-4 full charges of the iPhone from a completely dead battery. On the other hand, the Mophie Juice Pack Air is designed for those who are more concerned with a smaller and less obtrusive case-style battery that can be left on the iPhone, providing only 1200 mAh, or basically a single full charge of the iPhone’s own 1150 mAh battery.