I see mention of apps for phones, use this battery over that one, etc. Realistically this is ok, as if a battery dies you go home and get a new one.

What if - you are out in the tickie weeds and your battery powered whosis fails. I mean way out in the weeds. And your batteries are all dead and dying. What now?

Yes, I carry some spare batteries for devices. But mainly I refuse to rely on battery powered stuff. My emergency radio had a crank. My small emergency flashlight can recharge by solar. My watch is solar powered for that matter (I hate having a watch die in the field.) If it's dark, yes I have a flashlight, but I can also usually do most things without one (years of training as a grunt, sans NVGs).

So what's your plan if the batteries go out?