When it comes to draining the battery:
I have a “battery case” around my iPhone that gives me twice as much battery capacity as the phone’s built-in battery. I’m pretty sure they are available for other brands than iPhone.
A second option would be to use an “emergency battery” connected to the phone via a USB cable. Not so handy, but at least it’s extra battery.
For those who are shooting in the outback, there are larger solar panels that fit on the outside of a backpack.