To understand CPU Underclocking, let’s say a device comes with a  processor having 1600 MHz processing speed and you want to underclock it,  you will reduce it’s speed to 900 MHz or 800 MHz. That probably gives  you an idea about underclocking, basically it refers to slowing down or  restricting the speed of your device’s CPU to a lower number.  Underclocking is greatly effective as the battery life of your Android  device is directly linked with the user of your device’s CPU, so in case  you are not an Android freak and you don’t disturb your device much  with gaming and other such processes, you can underclock your Android  device to improve it’s battery life.
How to Underclock Zenfone 5:
- Root
 - Download and Install No-frills CPU Control
 - Max clock freq. set to 933 Mhz
 
Consequences :
- Lower antutu score and slower fps but good battery life
 
