In Settings (mine was under "More" from the initial screen.)
Find "Mobile Networks"
Go to "Network Mode"
Select from two choices: "LTE/CDMA" or "CDMA"
Choose "CDMA" that disables (though not really turning off) the 4G/LTE stuff. That single act will save you a crud load of battery. If you need 4G, then you can re-enable it as needed.
That is assuming you are on Verizon. If you are on another Carrier, they have the other versions there instead of CDMA.