While pondering what to do with the shattered kitchen scale, I got a bottom-dollar replacement touting its rechargeable lithium battery. After giving it the obligatory charge-before-using, I put it in service. Five days later, its battery was dead flat discharged.
So I gutted it to extract the battery:
It’s a cute little thing, isn’t it?
Much to my surprise, the obligatory battery rundown test showed it matches its 0.74 W·hr label:
We all know where this is going, right?
Crunche a connector on the battery, another on the scale, and make up a suitable current tap for a meter:
Which looked like this:
That’s about what I found for the craptastic scale running from a pair of CR2032 primary cells, so it’s not out of line.
Turn off the scale and measure the idle current:
Do you think I got a dud?
For all I know, the little microcontroller under the epoxy blob is running a continuous attack on my WiFi network, with the intent of siphoning off all my sensitive bits. Ya never know.
Dividing the battery’s 200 mA·hr rating by 4 mA says it really should be dead in 50 hours, which is close enough to five days: diagnosis confirmed!
Rather than fight, I switched to a battery with more capacity:
It’s long past its prime, but ought to last for a month, which is about as long as the shattered scale survived on a similar battery.
Sheesh & similar remarks.
The Smell of Molten Projects in the Morning 
Comments
6 responses to “Cheap Rechargeable Kitchen Scale: FAIL”
Your measurements piqued my curiosity about my digital scale that I purchased from Newegg about 15 years ago. It has capacitive touch buttons and uses one CR2032 battery, which tends to last about 5 months with multiple uses per day.
It draws 3.5mA when on, and just 8 microamps when off.
How can my scale possibly dissipate that much power when it’s off?
If it’s anything like my crappy Chinese digital calipers, the only thing the off button does is turn off the LCD display (which draws no power at all). That blue backlight could easily be the better part of your 4mA difference.
(Also, what, no Tek hall-effect current probe action? For shame!)
When the backlight is off it’s still drawing all that current: what can it be doing with that juice in there?
Dropping resistor to run a 1.2V microprocessor off of the 3.6V battery. :)
Or, perhaps slightly stupider but less absurd, self-heating effects in the strain gauge(s).
Aaaaand not flipping the proper
Sleep Modebits, so it’s running flat out in the dark …