I have built several first aid kits for prepping, and made a significant error. I bought digital thermometers, with spare batteries a decade ago when I started this journey. I recently needed one, and the battery was flat. I went to the spare battery, and it also was dead!
What I didn't think about (no excuse, I'm an Electrical engineer) is that the life expectancy in an LCD thermometer; is about the same as the shelf storage life on the same battery. Sadly, I KNOW this fact...and just didn't think!
So you can avoid this same problem:
Get an old fashion glass thermometer! This one will work every time, last fifty years, and will never run out of batteries.
Also; if you have one, you have none! This is the third buy of a pair of these for my prepping supplies. All kits now have a proper thermometer, with only these two needing delivery to the homestead.
I am working on converting all my prepping test equipment to 18650 LiIon battery packs. I will have no critical gear using disposable batteries...that's a recipe for disaster, that I can fix Now!
One unit needs 90 volts DC, so I will use a DC to DC converter to cut the size on the battery pack. Today is the time to get creative, before parts become difficult!
All this, from a failed thermometer. We must continually analyze our planning for glitches, to avoid all problems we can before hand! Because there will be things we missed, that will be easy to fix now; that will take great effort to fix later.
We need to out think disaster, faster than they can spend us into Oblivion!