you could be running a lot of apps in the background. Double click the home button and close all the apps running in the background.
if your brightness levels are high and you have location services, bluetooth etc all enabled and your wifi constantly enabled they will all drain your battery. if your not using it close them or turn them off...
also, your battery works on charging cycles as it has a "memory" only charge it when it is extremely low, and let it charge completely too 100% before taking it out else you'll damage the battery and make the lifespan smaller.
Almost all questionable advice, especially the battery advice. It is a bad idea to only charge the battery when it is low. Lithium chemistry batteries do NOT have a "memory"; that was only true of NiCd batteries, and no one uses them anymore. Lithium do not like to be fully discharged; you can charge it whenever you want. Here is Apple's battery advice: http://www.apple.com/batteries/
Location Services is not a significant battery user. It is one of the key features of the phone; why would you want to disable many of the key functions you bought the iPhone for? Better off getting a dumb flip phone if you use the iPhone with its best feature disabled. The confusion arises because apps that USE location services can use energy. But that's what you have those apps for. To use.
Set Brightness to automatic. It does an excellent job of adjusting the brightness to the ambient light conditions.
Bluetooth uses a vanishingly small amounts of energy, and nothing when no devices are connected. Turn it off if you have NO bluetooth devices to use it with, but otherwise it may make a difference of 5 minutes on a full charge.
The apps that you see when you double-click the HOME button are NOT running in background, except for things like streaming music, which you WANT running in background. They are suspended in memory so they will load faster when you need them.
i just got an Iphone 4 battery does not last 12 hours?
It depends on what you are doing with it. Here are the power specs for the iPhone 4:
- Talk time: Up to 7 hours on 3G, up to 14 hours on 2G (GSM)
- Standby time: Up to 300 hours
- Internet use: Up to 6 hours on 3G, up to 10 hours on Wi-Fi
- Video playback: Up to 10 hours
- Audio playback: Up to 40 hours
Match these to your usage and tell us which one is missed.