How long is the maximum battery life of each iPhone?

The maximum battery life for each iPhone model can vary considerably depending on how it used -- for phone calls, for Internet over wi-fi, Internet over EDGE or 3G networks, music playback, video playback, and so forth -- but EveryiPhone.com lists the maximum battery life for each task, as estimated by Apple, on the specs page for each device.

For objective battery life test results from a variety of third-parties, you may also find the following Q&As useful:

• What is the battery life of the iPhone 4S in "real-world" tests? Is the battery replaceable?
• What is the battery life of the iPhone 4 in "real-world" tests? Is the battery replaceable?
• How does the battery life of the iPhone 3GS compare to the iPhone 3G in "real-world" tests? Is the battery replaceable?
• How does the battery life of the iPhone 3G compare to the original iPhone in "real-world" tests? Can you replace the battery?
• What is the battery life of the original iPhone? Can you replace the battery?

Why won't my iPhone battery charge completely? Why does my iPhone run out of power so quickly?

If your iPhone battery isn't charging completely or the battery life suddenly seems like it is running out of power more quickly than it used to, Apple recommends that one try restarting the device and if that doesn't work try restoring it. Please note that restoring the iPhone will erase all data. Be sure that you have recently backed up your iPhone before restoring it.

If this doesn't solve the problem -- particularly if the iPhone is a couple of years old -- in all likelihood the battery has reached the end of its useful life and needs to be replaced.

Also see:

• How can I conserve my iPhone's battery life?
• How do I replace the battery in the original iPhone (2G)?
• How do I replace the battery in the iPhone 3G and iPhone 3GS?
• How do I replace the battery in the iPhone 4?

How can I conserve my iPhone's battery life?

Apple's own site features a helpful document of "commonsense pointers" to help conserve and extend the runtime of the iPhone as well as prolong the life of the battery. Such tips include updating to the latest software (as Apple routinely tweaks battery performance), optimizing your settings in ways to reduce power consumption, locking your iPhone when not in use (so the screen isn't drawing power when it isn't being used), and using the device regularly, along with other helpful advice.

BatteryUniversity.com additionally provides some additional tips on how to prolong lithium-based batteries, like those used in the iPhone models, that also may be of interest.