3 X Battery Saver – iBattery By Azoine Tools
"iBattery" is a simplest, easiest and yet the most powerful battery charge saving App! This App saves your battery by disconnecting an Internet connection while in sleep mode. "iBattery" got more positive reviews in Japan than "JuiceDefender", because it doesn't just disconnect from the Internet, but also ends all the running Apps.
Furthermore, at a chosen battery level phone can be automatically switched to Flight Mode, making you chances of running out of battery even lower. (This feature is available on Android 4.1 and earlier)
If you phone's coverage is unstable you'll be able to save even more battery power!
Cautions and other info
・iBattery disconnects your phone from the Internet while in sleep mode.