I am experiencing enormous battery drain on my iPhone when flying my Inspire.
I am quite surprised that the RC does not provide a certain amount of power to the connected device.
Not for charging, but slower draining pace...
The RC itself has a lot of running time and would be able to provide a bit in order to ensure running time for the connected device as well...

iOS devices are very specific about the current needed to charge their devices: https://support.apple.com/en-us/HT201569 -> the RC doesn't pack enough juice!

However, this thread does provide some pretty good configuration background to turn off the iOS stuff that's consuming your electrons: http://www.phantompilots.com/thr ... -performance.48388/

Thanks to InspireHelp/PhantomHelp

Well the live view of 720p consumes a lot of power on both android and IOS... close all the apps, turn of WiFi Bluetooth and all the things you don't need during the flight, it will save you some power