[Galaxy S III Themes and Apps] eugene373:
Script Version!

This time I present to you a script that will in theory (and so far for me, in reality) save us some battery without having to risk our hardware with undervolting! I present to you...

CPU Sleeper

What is it?

Its a fairly simple script that will put CPU 1 OFFLINE when the screen turns off. Once the screen comes back on, it will allow CPU 1 back ONLINE.

How does it work?

Since we have dual core CPUs, we have a CPU 0 and a CPU 1, core 1 and core 2, while the screen is off we really only need to have 1 core active, this script will make sure CPU 1 shuts off while the screen is off, then resumes normal usage when the screen comes back on.

WARNING! READ THIS!

This script relies on init.d OR script manager! CM9, for some reason, tends to run this at the exact same time it runs some other script (I forget atm which) and it will clash, causing no boot! CM9 users MUST use the script manager version install! Flex Reaper appears to work fine with it as init.d. I strongly urge you to use the script manager version of this, NOT the flashable version. Always make a nandroid backup before modifying the system, including this!

Instructions

Available in 2 versions, script only version which you can place wherever you want and run however you want, or a CWM/TWRP flashable zip that will place the file for you in /system/etc/init.d and set permissions.

Version 1: Flashable

Same as any of my flashable releases, I did most of the work for you!

Make a full backup

Download to external SD card

Install from SD card

Pick the cpu sleeper zip file

it'll be almost instant

reboot

Shouldn't be any need to clear caches or anything like that.

Version 2: Script only

This can be run in 2 ways, via init.d support, or via script manager. Both are pretty similar, and can be done a number of ways, however this is the basis of how.

Init.d supported kernel:

Make a backup!

Download the script file, making sure no extensions get added onto the file. Copy the file to /system/etc/init.d and set the permissions to the following:

XOX

XOX

XOX

Once done, reboot the system, and it will take effect when your system is finished rebooting.

Script Manager

This method is probably the better method, and should work with any kernel/ROM. Download the script file, making sure no file extensions get added, and copy it to /system/etc. Set the file permissions to:

XOX

XOX

XOX

Once done, load up script manager, select browse as root (if it isn't already set from the crossix mod method in the guide) then browse to /system/etc and select the script file S98cpu_sleep, then select ROOT and BOOT options. After this is set, reboot system.

What do I do if I can't boot after using this?

You made that backup, right? Ok, then here is what you do.

Hold the power button until the tablet powers off

Press and hold the volume down button, next to the screen lock switch

Press and hold Power (while holding volume down)

Once the recover kernel message comes up, release the buttons

In CWM go to advanced, mounts, mount system, then format system

In TWRP, go to wipe, then wipe system

In CWM go to restore, advanced restore, restore ONLY system

In TWRP select restore, then uncheck all so ONLY system is checked

After restoring system, wipe cache and dalvik cache, then reboot system.

System should boot normally.

Downloads

Available in 2 versions, script only version which you can place wherever you want and run however you want, or a CWM/TWRP flashable zip that will place the file for you in /system/etc/init.d and set permissions.

Dual Core:

Download: Script Only - Recommend Install via Script Manager App

CPU Sleeper script only

Quad Core:

Download: Script Only - Recommend Install via Script Manager App

cpusleep

Thanks to pio_masaki for rewriting the OP