Energize!

http://www.apple.com/batteries/iphone.html

Charging Tips

iPhone 3G and iPhone 3GS cannot be charged with a FireWire power adapter or FireWire-based car charger. Make sure your computer is on while charging iPhone via USB. If iPhone is connected to a computer that’s turned off or is in sleep or standby mode, the iPhone battery may drain.

Maximum Battery Life¹

iPhone 4 offers up to 7 hours of talk time on 3G, 14 hours of talk time on 2G (GSM model only), 6 hours of Internet use on 3G, 10 hours of Internet use on Wi-Fi, 10 hours of video playback, or 40 hours of audio playback on a full charge at original capacity. In addition, iPhone 4 features up to 300 hours of standby time.

Charge Cycles

A properly maintained iPhone battery is designed to retain up to 80% of its original capacity at 400 full charge and discharge cycles. You may choose to replace your battery when it no longer holds sufficient charge to meet your needs.

Let It Breathe

Charging your iPhone while in certain carrying cases may generate excess heat, which can affect battery capacity. If you notice that your iPhone gets hot when you charge it, take it out of its case first.