Top 15 ways to increase iPhone 3G battery life

1. Update to the Latest Software. Apple regularly release new firmware for the iPhone that could increase your battery life. Also make sure 3rd party apps are also up to date.

2. Minimise the use of location services. Applications that actively use location services such as Maps may reduce battery life. To disable location services, go to Settings > General > Location Services and use location services only when needed.

3. Fetch new data less frequently. Applications such as Mail can be set to fetch data at specific intervals. The more frequently email or other data is fetched, the power your iPhone will use checking those accounts. To fetch new data manually, from the Home screen choose Settings > Fetch New Data and select Manually. To change the fetch interval, go to Settings > Fetch New Data and select a less frequent time. Note that this is a global setting and applies to all applications that do not support push services

4. Turn off push mail. If you have a push mail account such as Yahoo!, MobileMe or Microsoft Exchange, turn off push mail when you don't need it. Go to Settings > Fetch New Data and set Push to Off. Messages sent to your push email accounts will now be received on your phone based on the global Fetch setting rather than as they arrive.

5. Use fewer email accounts: You can save power by checking fewer email accounts. This can be done by simply turning off an email account or delete it. Some email accounts allow you to combine all your other accounts into one email address, which will help to reduce power usage and improve battery life.

To turn off an account, go to Settings > Mail, Contacts, Calendars, choose an email account, and set Account to Off. To remove an account, go to Settings > Mail, Contacts, Calendars, choose an email account, and select Delete Account.
Minimize use of third-party applications: Excessive use of applications such as games that prevent the screen from dimming or shutting off or applications that use location services can reduce battery life.

6. Turn off Wi-Fi. If you rarely use Wi-Fi, you can turn it off to save power. Go to Settings > Wi-Fi and set Wi-Fi to Off. Note that if you frequently use your iPhone to browse the web, battery life may be improved by using Wi-Fi instead of using cellular data networks such as 3G or Edge.

7. Turn off Bluetooth. If you rarely use a Bluetooth or anything that uses it, you can turn it off to save power, since Bluetooth can drain the battery quicker than you think. Go to Settings > General > Bluetooth and set Bluetooth to Off.

8. Use Airplane Mode in low- or no-coverage areas. Your iPhone always tries to maintain a connection with the cellular network, so it may use more power in low- or no-coverage areas, since it will always be looking for a connection. Turning on Airplane Mode can increase battery life in these situations. Please note that you will be unable to make or receive calls. To turn on Airplane Mode, go to Settings and set Airplane Mode to On.

9. Lower screen brightness. Dimming the screen is another way to extend battery life. Go to Settings > Brightness and drag the slider to the left to lower the default screen brightness. In addition, turning on Auto-Brightness allows the screen to adjust its brightness based on current lighting conditions. Go to Settings > Brightness and set Auto-Brightness to On.

However, to further improve battery life turn Auto-Brightness off and set the brightness manually, this way the iPhone doesn't have to use the brightness sensor to monitor brightness levels.

10. Turn off EQ. Applying an equalizer setting to song playback on your iPhone can decrease battery life. To turn EQ off, go to Settings > iPod > EQ and select Off. Note that if you've added EQ to songs directly in iTunes, you'll need to set EQ on iPhone to Flat in order to have the same effect as Off because iPhone keeps your iTunes settings intact. Go to Settings > iPod > EQ and tap Flat.

11. Turn off 3G. Using 3G cellular networks loads data faster, but may also decrease battery life, especially in areas with limited 3G coverage. To disable 3G, from the Home screen choose Settings > General > Network and set Enable 3G to Off. You will still be able to make and receive calls and access cellular data networks via EDGE or GPRS where available.

12. Use sleep mode. Sleep mode on the iPhone puts it into a low power state, since turning it on uses a lot of power, but resuming from a standby state uses a lot less and could help your battery to last longer.

13. Use Auto-lock. Using auto-lock ensures your iPhone is locked and switches the screen off, saving you battery. You can change Auto-lock setting by going into Settings > General > Auto-Lock and set it to 1-3 minutes. I would recommend setting to 1 minute to ensure maximum battery life.

14. Exercise the battery. By exercising the battery you can help to retain your battery capacity, and give you longer battery life. To exercise the battery you need to run the iPhone until the battery is almost flat (the lower the better) then recharge the device to 100% and it should improve your battery life. I would recommend exercising the battery once to three times per month depending on usage.

15. Avoid excessive heat. The iPhone's battery will discharge quicker when exposed to lots of heat, since the Lithium Ion battery is sensitive to extreme heat above around 110 degrees Fahrenheit, so leave it out of sunlight as it will reach that temperature quickly, and it can actually reduce your battery capacity if exposed for long periods of time.