Scales that refuse to measure if the battery isn't brand new
I hate this scale, it says low battery and shuts off after just 3 months of sitting in the drawer. It infuriates me that there's still a lot of energy in the battery, I can use that in remote controls with no issues
If there's enough battery to say "low battery", then there's enough battery to show the measurements!
Normal AA or AAA battery, or a CR<something> button? If it is a button cell, try wiping it with alcohol before you insert it. Many modern button cells have a coating that tastes horrible to prevent people (children) from taking them into the mouth. I've noticed that on some brands, this coating measurably increases the resistance of the cell, not only reducing the the power it can deliver, but als making it appear "emptier" than they are ofor the measuring circuits. Wiping off the coating with alcohol (90% isopropanol) expanded the cells' life (in a kitchen scale to boot!) significantly.
My cheap scale will not work with my freshly recharged amazon basics AAAs. Apparently those do not hold up well enough under load. And of course any set of batteries that does work, discharges over a few months.
So I just bought a cheap mechanical scale (not from Amazon) and I eyeball it for weights under 50g. Good enough and dead reliable.
This may or may not help, but a nickel is very close to 5 grams. You may be able to slap something silly together with a bunch of nickels taped together :P