Is there an option to turn off data/prevent data use when not on wifi?
I use the widget in Battery Doctor to handle that manually.
You can also just pull down the Notification bar and touch the DATA indicator and that will toggle it off.
Personally, if you look at my signature line, I use MacroDroid to turn off Data and WiFi when the phone is sleeping (screen locked)
Then, when I unlock the phone, MacroDroid senses that and turns the internet back on for me.
My reasoning is, the internet is NOT needed if I am not using the phone. This stops any background activities from polling social apps, weather reports, downloading useless email garbage.
When I unlock the phone, the internet is ON in about 2 seconds and my email titles are loaded up before I can even toggle the app icon to read them.
The end result is, the battery life is stupendous! If the phone is idle and on standby only. It will go a week without being charged.
That means, that regardless of how long it has been since I took it off charger, the battery will still have plenty of power to do anything I want.