[Galaxy S III General] stanley08:
This method is the best I figured out and it works pretty well!

I discovered the main cause of battery drain on JB is the 'Media Scanner'. I dont know exactly what the issue is, but it DRAINS your battery! I thought it was a corrupt file in my phone that was causing Media scanner to get stuck and scan for loong periods instead of 2 - 3 minutes which it should take regularly. (btw media scanner is launched every time you restart your mobo or make changes to your media files as far as i know). I formatted both my Internal and External SDs but it still didnt help. Now use the following Steps below to solve these issues.

1. Download Media scanner ROOT.

This app - https://play.google.com/store/apps/details?id=com.addz.mediascannerroot

2. Download Media scanner also

This one - https://play.google.com/store/apps/details?id=com.addz.mediascanner

3. Always set 'Power saving' option on phone on. I can assure you that you'll hardly notice the difference in performance when you turn on power saving.

Having said that, if you want more brightness, you can increase from toggle or just tick auto by the side of brightness level settings right there in your notification bar.

Also, if you need to game or use heavy app that require alot of system resources, just turn off power saving.(Because power saving slows down your processors Maximum state)

How to use the apps mentioned in numbers 1 and 2.

First one is to stop it (Media scanner) from ever scanning. So open that one with ROOT at the end of the name (Grant SU prompt), then hit disable media scanner button wait for it to work. Just one or two seconds.

Sometimes you might open your gallery and notice a file is missing or you might not see even a single picture or vid in it.

ONLY NOW! can you open the second app dat DOESN'T contain ROOT at the end of its name.

Just open it and then hit the back button to close. thats all!

What this does if to call the media scanner you disabled earlier with first app so it can scan your SD Cards and your gallery will display your files.

You can read the application descriptions on Play store for better understanding.

If you notice that these steps still doesn't help you with your battery drain issue, try disabling Motions and Animations in debugging options too. Both in settings. Then test battery again and see how good it works.

IMPORTANT: You also want to change PhilZ recovery Backup format from .dup to .tar as this might be the reason why Media scanner goes crazy. How to - Reboot into recovery, select Backup and restore, then select 'Choose backup format', then hit tar. Now delete all previous backups done in .dup format and then hit 'Free Unused backup Data' or go into phone, delete the folders of the backups done in .dup and then delete evreything in blobs folder. Now do a fresh Nandroid which will now be in .tar format. ( Always Have a Nandroid backup on your phone , it can come in handy! :D )

REMEMBER: What works for one person, might not exactly work for everyone. Everyone does have 100% same hardware. :) .So take it easy while throwing your shots at me. :D I just decided to share this.

I hope this helps some solve their battery issue.

Please hit thanks if this helps you.