1. Turn off Wi-Fi
Only use Wi-Fi when you're at home, or when you really need it, at a public hotspot. The rest of the time, the Wi-Fi antenna is constantly searching for a signal, thus draining your battery.
2. Turn off UMTS/3G
The talk time doubles to 10 hours max. if you only use the GSM antenna. The internet is not accessible when you turn off Wi-Fi and 3G, so turn it back on when you want to go online.
3. Turn off Bluetooth
Just like the Wi-Fi antenna, this antenna is constantly searching for a connection when turned on too. Again, only turn it on when you need it.
4. De-activate the GPS-antenna
You only use this feature with certain applications like Google Maps, G-Park and Airme. Again, the rest of the time, the antenna is constantly trying to make a connection to a satellite without any use.
5. Brightness of the screen
Although a bright screen looks very nice, it's killing your battery. Turn off the automatic brightness option and manually set it at a low but acceptable level.
6. Check your e-mail manually
The default setting for e-mail is "Push", which means your phone automaticly checks for new e-mail at set times. If you turn this feature off, your phone won't try to make a connection every now and then. If you check manually, you can do it at larger intervals or only when you have the time to read your mail.
7. Is auto-lock turned on?
Yes? Good! Change the time for this to one minute instead of the default five. This way, your battery sucking screen isn't on any longer than necessary.
8. Turn off the rumble function
There are many games available for your iPhone. Many of these games support your phone's rumble function. However, this will drain your battery very fast. So, turn off the rumble when playing games.
9. Don't use the App Store
Don't download your applications at the App Store, instead use iTunes. This way, you won't make use of your 3G antenna, again resulting in a longer battery time
10. Long term use
Completely drain your battery and fully recharge it once a month. This increases the lifetime of your battery greatly.