How to turn off 3G or 4G LTE off on Android in order to save battery
1. Turn off 4G LTE on the HTC One M8
2. Turn off 4G LTE on the LG G3
3. Turn off 4G LTE on the Samsung Galaxy Note 4
Go to Settings > Connections (tab) > More networks > Mobile networks > Network mode > choose "WCDMA/GSM (auto connect)" or "GSM only". The first option will allow your Note 4 to always stay online by reverting to the 2G GSM network if needed, while the latter will downgrade all the way to 2G only and not go any higher. This means that your mobile data speeds will be capped at about 128kbps, but you'll be saving the most battery and those speeds are still enough to keep IM's and e-mails coming through.
4. How to turn off 4G LTE on the Oppo Find 7
Go to Settings > General (tab) > Mobile networks > Network Mode > chosee "WCDMA only" or "GSM only". In case you're wondering, WCDMA is 3G, and GSM is your 2G network. If you live in the States and are on Verizon, Sprint, or U.S. Cellular, then you'll see just "CDMA" instead of WCDMA – it's still 3G, just a different standard.