I posted this before and I am posting this again.
How to save battery life
Check my post about tricks and menu options for a more detailed list.
You may also want to check your application settings and use the phones battery use monitor as it will also give you additional information as to what is using your battery. Even with an application monitor, you may not always be able to see what is draining your battery.
Message was edited by: Markie_B
Turning off WiFi is not a good idea. IF you have a WiFi connection, always use it. It will save tremendous battery life. Being on Sprint's network for data will consume battery quickly.
I would not worry about using the application monitor to end apps. You are most likely causing worse battery life by doing this, Android knows how to use resources and by ending them prematurely, you cause them to consume more power when the OS needs to restart them.
Things that kill battery life are accounts that sync like Facebook, Twitter, etc. so just be aware of those as well. Also, make sure you are on CDMA only as Markie_B posted.
I apologize that you are having issues with the battery life on your Galaxy III. You may want to make sure that your network settings are not set to LTE/CDMA. It should at this time be set to CDMA only. From your home screen you should select Menu> Settings> More Settings> Mobile Networks> Network mode> and make sure it is selected to CDMA and not CDMA/LTE. Please let us know if you continue to have battery issues.