You should consider making an "emergency mode" for the iPhone. This could work like the Apple Watch on low battery... when the phone is below a certain percentage (20%), users can turn this mode on which makes the phone only a phone to make calls. (Similar to how the Apple Watch becomes just a watch) Maybe have 2 contacts on speed dial and a regular key pad to dial 911 or other number. Point is, eliminate everything else... and save the left over batter for emergency use only (making calls). OLED would save battery because only certain pixels would be lit up. LTE wouldn't be needed and only a cell phone signal needed (consumes less energey). The lower power mode on the watch extends the life by 24+ hours. Who's with me?