Just about the most important tips made available from users and experts alike is to regulate the temperature in which the iPhone operates. The lithium-ion (Li-ion) battery of the iPhone functions very best in temperatures ranging from 32 to 95 degrees Fahrenheit, or 0 to 35 degrees Celsius. At its extremities, the iPhone can continue to function between -4 and 113 degrees (-20 to 45 degrees Celsius) but temperatures beyond these ranges will be detrimental to your iPhone battery. Put simply, leaving your iPhone in the freezer or in a hot car is probably not advisable. Keep it out of sunshine as well. - battery
This next tip culled from forums and the like is not so clear-cut. There are some who claim that allowing the iPhone battery to totally discharge more than once monthly is not advisable, while others believe that no harm can come of it. What appears to have a consensus would be that the iPhone battery must be fully discharged from your full a discharge once per month in order to reset battery meter.
It is also beneficial to have an idea of your actual usage plus your battery life in order that you can more grasp your options. You can view your usage statistics inside the Settings Menu underneath the General Tab then Usage. You will observe Usage, which is the time the iPhone was in active mode and that means you were on a call, watching a relevant video, listening to music, browsing the Internet, and so on. It will also show your Standby time, which is the total amount of time the iPhone has been running from its last full charge, whether in active mode or not. Usage divided by Standby time will give you a percentage of the time you're actively using your iPhone. The bigger this percentage, a lot more you will need to charge your iPhone, so plan accordingly.
Updating to the latest official version of the software using iTunes will let you with taking care of the iPhone battery, but that's still up for grabs. Some users complain that the update from three to 3.1 wreaked havoc on some applications. However, updates and patches should help improve the performance, so maybe that last one was obviously a bit of a fluke. At any rate, before updating your software, check out the forums to see what are the feedback is from those who have already updated their software.
And of course, the old standby of utilizing on the applications you need, turning off push, 3G and reducing the brightness of the display etc are still part and parcel of maintaining your iPhone battery in good health for a longer period. Just because you've probably heard it before doesn't mean it doesn't work.
Something totally new, though. Some users have seen that proximity with a cell tower (thus providing use of a strong signal) extends it life. This may be because network searching is taken to a minimum. So attempt to stay in areas with a decent signal. A last and final tip is to use your iPhone regularly, which means you massage the kinks out of the system and become knowledgeable about the peculiarities of your particular unit. All things considered, your phone is really a highly personal gadget, and really should be treated as a result. - battery