This is obvious, but how big a difference it makes was a revelation.
Even though my iPhone was in constant use for three hours, during which I mostly read or typed, the battery level only went down by about 20 per cent. Normally, such constant use would send the battery meter down a lot more, perhaps 40 or 50 per cent. The reason for the low power draw was because, I am fairly sure, I was on an airplane and my iPhone was in airplane mode. That mode turns off power-hungry cellular, Wi-Fi and GPS connections.
Other ways of conserving battery power that I’ve found to be effective are to turn down screen brightness and changing the get-mail function to manual or just once an hour, instead of having the device checking constantly.
If you take the snarky view, regard these measures as hobbling your device. Or you can regard it as balancing your needs. You need power to last longer, so you turn off things you do not need.
You could also get yourself an external backup battery.
