You might be looking to disable 4G/LTE on your Samsung Galaxy S3 device to maximize battery life. You can disable 4G/LTE On Samsung Galaxy S3 by folowing below mentioned steps.
1. First select Settings from the app list.
2. Now select Data usage (More…)
3. Now tap Mobile networks.
4. Now choose Network mode.
5. Now choose the CDMA setting.
With this selection, your Galaxy S3 device will connect only to the 3G network. Anytime if you feel to use 4G, simply switch the setting back to LTE / CDMA.