iPhone power saving details
These are idea’s to pursue, if you need to satisfy the inner scientist try each one out to see what nets you the most benefits. Newer devices won’t benefit as much.
You can always enable Low Power Mode which does other changes and is simpler that help extend battery charge without changing anything listed below.
iOS 11.0 had power draw issues out the gate for my iPhone 6S+
If Possible get the latest iOS 11.2, lots of fixes here.
Bluetooth when it’s on, and on older devices, it uses more power, especially in a noisy Bluetooth environment. You can check to see what is going on with a BLE app like LightBlue. That is only half the story as its only the low energy.
Old 2.4Ghz network mode will work the best for battery life. This is like 3G 4G mode.
The 5Ghz modes will really drain the power. This is like LTE.
If you have access to the Wifi router, you can enable some power saving features for Wifi, you can explore if your router has that option (not to mention QoS that supports better VoIP quality.). The feature Called WMM or WMM APSD
And yes, you can turn off Voice over LTE, and in some cases turn off LTE altogether if you want to see the battery last longer.
Turning off Voice over LTE will prevent LTE to Wifi handoff, where the phone can hand off a voice call between the two.
All iPhone, iPad and iPod touch devices with iOS 9.3.5 and lower, and AppleTV devices with version 7.2.2 and lower are affected by the remote code execution vulnerability(and iOS 10 and later the breach is fixed)