Scales that refuse to measure if the battery isn't brand new

That's because of the way these scales work. They use a material that deforms under stress and when it deforms the resistance changes. By putting current through this material and measuring the voltage drop, it can be mapped to how much stress the material is under and thus how much weight is on the scale.

This is a pretty roundabout way and has a lot of caveats, but it is very cheap. So cheap scales always work this way. That's why they aren't super accurate and have deviations depending on things like temperature. Another big downside is any permanent deformation ruins the calibration, giving incorrect results. That's why you never put more weight on kitchen scales than it says, it will break them.

The issue you are running into is the way it measures. It applies a very specific voltage and current in order to get the result. The lookup table it uses is only valid within a narrow range. When the battery voltage goes outside that range, it can no longer perform the measurement. Even though there's plenty of juice for things like the little processing chip and the LCD display. They don't need a lot of power and can do with low voltages. But it can no longer weigh anything so it just errors out with a low battery warning.

This is probably not what you wanna hear, but when the battery gets low, the current gets weaker. If the current gets too weak, the scale becomes more and more inaccurate. Like, wildly so. In other words, the alternative is to lie to you. Badly.

That's not really how it works. The components of the scale require a certain amount of current especially if it's digital in nature. As a battery approaches being drained, it produces less current. Less current can often power an analog device to a lesser degree, like lighting up an indicator light or LCD or even the IR LED light on a remote, just very dimly. But the tolerance of the weighing components is probably much less than the tolerance of the LCD panel or LED bulb. So many devices use an LCD or indicator LED bulb to show that the device isn't necessarily broken, it just needs new batteries.

If it's sitting in a drawer and getting drained, then it's probably not turned off properly or it may be the type that turns on automatically when it gets pressed down and inside the drawer it's getting activated. Instead try taking the batteries out of any device that sits around for a long time without use. It will prevent accidental draining and also reduction the likelihood that the batteries will leak after a time. I usually pop the batteries part way out or put them in a small bag that I attach to the device with tape or a twist tie. Just make sure they aren't touching anything metal and that the poles aren't touching each other. Batteries will lose charge over time, but with alkaline batteries, that's usually years, not months. Rechargeables generally take much less time, though.

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I have the same scale and bought a few rechargable ithium-Ion AAAs and they work line a charm having a constant voltage until empty.

Only downside is that you don't get any warning when they are about to run.

(Something like that: https://www.mediamarkt.de/de/product/_verico-verico-li-ion-akku-loop-energy-aaa-mit-usb-c-buchse-2er-pack-lithium-ionen-akku-109861637.html )

Edit: nvm, just saw your comment about yours usung a coin cell it seems like there are some deviations between different models of the scale.

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.

CR2032 batteries are hit and miss in my experience. Sometimes my car FOB burns through one a month2 and other times they'll last years.

I know this isn't helping but your scale is saying "ok lol"

For decades scales worked just fine without any electricity. Maybe get one of those.

I replaced mine with a usb cable. No batteries.

My scale looks similar to this. If I leave it on it goes into sleep mode which still drains power slowly but turn on instantly as soon as there is weight on it. If I hold the power button when I'm done it turns off and makes a beep and then I have no issues turning it back on months later. Still on original batteries after 2 years.

I have a scale that charges with usb-c. It's also accurate to 0.1g

Didn't think you were going to get a bunch of nerds telling you exactly why it works this way 🙄

I have to charge the battery EVERY TIME! There is a wheel on the top I have to spin else it won't do ANYTHING.

Infuriating

I believe I have this exact same scale, and I also hate it. My main problem is that those capacitative buttons sometimes refuse to work, and it's real nice when I'm trying to measure something in grams and it randomly gets stuck in pounds.

Buy an analog, non digital scale. That piece of junk is just e-waste.