For smartphone users, battery saving is a critical issue.
If battery is exhausted, your attractive smartphone will turn into a heavy block.
I use Galaxy S III by Samsung. This model is equipped a battery with 2,100mAh. This is relatively rich but not satisfactory. When I use Galaxy S III for internet browsing and e-mail checking, the battery cannot last full day. I have never used an iPhone but the situation is similar I guess.
So, I decided to introduce some application to save battery.
In general, battery-saving applications are classified into 2 categories; functional modulator and connection shutter. Some applications equip both functions.
Functional modulators modify automatically some function of smartphones. For example, they darken the touch screen, shut down blue tooth, and kill other active applications. I tried some of them. However, the effect on battery life is unclear. To begin with, I usually turn off any functions manually after using. Moreover, these applications often work erroneously. I have experienced that I could not turn off Wi-Fi of my smartphone.
The latter is stronger. This type of application makes smartphone disconnect to the internet (also 3G connections) continually. Synchronizing is made by a certain minute. You know that network connection consumes battery severely. So these applications can save battery effectively.
One disadvantage is loss of immediate connection. I tried Juice Defender, Deep Sleep, and others. All of them are not able to receive e-mail offered by mobile phone companies (Sp-mode mail by NTT DoCoMo) just in time. Some applications equip white list system, with which you can register some applications whose connections are not interrupted by the application. But these systems did not work correctly, as far as I tried.
After some trials and errors, I adopted Green Power. This application equips both functions above. I disabled synchronizing but let 3G connection free. The Battery lasts almost one day.
If you know more excellent application, please tell me about it.