Gary from iPhoneInCanada.ca was a little miffed with the battery performance on his iPhone 3G -- down to 20% after some "light surfing and barely any talking" -- so he set out to see what he could do about it. One of the major things you can do to save battery life is to turn off the 3G when you don't need it. This almost eliminates the appeal of the iPhone 3G, but you can always activate it again if you want it. Other tips include turning off the auto-brightness, turning off location services, turning off Wi-Fi, turn off Bluetooth, and severely limit your use of GPS. Alternatively, you can get a massive USB extension cable for continuous charging.

How to Increase Your iPhone 3G Battery Life - the Extreme Edition

- Turn on 3G only when you need it. I found that having 3G turned OFF saved battery life (duh!). Using EDGE actually isn't that painful–just think of it as a mildly disfunctional WiFi hotspot!
- Turn off Location Services.
- Turn off Auto-Brightness. Manually move the slider to 25% or 33% brightness.
- Turn off WiFi until you need a hotspot. The iPhone's WiFi will automatically try connecting to SSIDs it detects.
- Turn off Push. Change your Fetch schedule to Manually.
- Set Auto-Lock to 1 minute.
- Turn off Bluetooth.
- Limit GPS use unless you really need it.
- Do a monthly battery calibration. According to the Apple website, you should be doing this periodically. Give your iPhone a full charge, then let the battery run out. Recharge.
- Usually with lithium-ion batteries this is not necessary as they maintain no "memory effect"...but it's worth a shot.
- Only use the iPhone 3G connected to an outlet. Find a 100ft extension cable and attach it to your USB cable. Attach USB cable to iPhone 3G. Let extension cable follow you around the house, knocking furniture, pets, and children over. Ignore wife/girlfriend's complaints because–email, Twitter, and the iPhoneinCanada.ca forums call for your attention.
- The bottom line is Apple needs to desperately release an update for 2.0 firmware. When previous updates were made, such as jumping from 1.0.2 to 1.1.1, battery life increased. Let's hope a new firmware will help increase battery life by a bit.