Lately I've had some obviously inaccurate measurements from my Timemore Black Mirror scale. That would happen occasionally but not always. I was charging it today and as luck would have it, I was sitting beside it. I typically charge it unattended. I noticed that it took a very long time to charge and multiple times it seemed to restart charging. I grabbed it to check the cable and noticed it was quite warm in one spot. I though - that's alright, it's likely where the battery cell is, it's charging, lithium cells get warm during charging. Later I took it off the charger and while handling it I examined the hot spot a bit more. I noticed that when I squeezed the scale at that corner, the top plate wouldn't sink towards the bottom as it does in the other corners. A few mental calculations later I figured this could be a swollen cell that has grown so large that it impacts the plates and doesn't let them come together as they do normally. I took it apart. Lo and behold this spicy pillow:
The marking on it means it's supposed to be 8mm thick. It's currently closer to 12.5mm. Removing the battery allowed the two plates to come together in all corners as normal. That confirmed the hypothesis. Further, the reason why it only occasionally impacted the measurements is likely due to the weight of the cup I was using. When using a lighter cup, the total weight would be lower than needed to get the two plate to touch the battery and produce inaccurate measurement.
I ordered this as a replacement. It fits the dimensions and it's got some safety certification.
To check if your scale is a fire hazard, squeeze this corner:
Normal squeeze action looks like this. Unfortunately I didn't record a video prior to removing the battery.
If it the two plates come together as the do in the other corners, you're probably okay. If the plates don't come nearly as close, you've got an unlit petard in your hands.
TBH, this is a risk for all "value" devices that don't have to pass NA/EU electrical certification. No cert means the cell can be whatever part was cheap and alright enough. Longer term reliability without specific testing isn't obvious. Every now and then I fall into the rabbit hole of trying to remember all the different devices with potentially questionable cells. The occasion today is likely to trigger another sweep.
The cable that came with my cheap scale is borderline e-waste. The resistance of that abomination is many times higher than with any USB cable I’ve ever measured, so it’s pretty clear which corners were cut in production. I wonder how bad the battery is though… Better be careful when charging it.