The Average Battery Life of an iPhoneby Andrew Mikael
The iPhone's large display, networking features and powerful processor all take a toll on battery life, and the length of life on a single charge depends largely on how much you access these features. Moderate use can get a single charge through more than a day, while heavy use shortens the effective life to a small fraction of a day. As with all rechargeable batteries, the lifespan of a charge will decrease as the iPhone ages.
Apple advertises up to 300 hours of life for an iPhone 4 device kept in standby, without making any calls or running any applications. For practical use, Engadget found the battery of a new iPhone to last for almost 40 hours while under frequent use of a variety of features. Constant use of the iPhone's more resource-intensive features such as gaming, video recording or video calls can drain the battery in as little as four hours.
Battery Life Over Time
Rechargeable batteries lose their capacity slowly over time. Apple estimates an iPhone battery to still retain approximately 80 percent of its original capacity after 400 recharging cycles. More recharge cycles will further decrease the capacity. To minimize the capacity loss, fully drain and recharge the battery at least once every month.
Improving Battery Life
Apple recommends several usage behaviors to maximize the battery life of an iPhone. Keep the phone as near as possible to room temperature, and avoid exposing it to extreme heat or cold. Turn off GPS, email auto-check, Bluetooth and other networking features when not in use to avoid draining the battery needlessly. When out of coverage areas, place the iPhone in Airplane Mode to stop the device from constantly searching for signal. Use the dimmest available screen brightness, or use the Auto-Brightness setting. Finally, keep the iPhone locked when not in use to turn off the screen.
Replacing Old Batteries
Apple provides a replacement program for batteries that no longer hold a satisfactory charge. For iPhones still under warranty, Apple will replace the battery if it no longer holds 50 percent of its original charge. Apple performs out-of-warranty replacements for a fee. Other companies also offer battery replacement and do-it-yourself kits, but note using these services will void the iPhone's warranty.