This device tests batteries of various types -- button cell, AAA, AA, C, D, and N; coin cell lithium; and 9 volt packs. It supports battery chemistry of alkaline or NiMH types for most cells.
The knob selects the cell size and chemistry, then is clicked to start a load test with the appropriate current. The voltage under load is measured, and the display shows "New/Good/Weak/Dead" according to the corresponding voltage threshold. The estimated charge level is displayed, as is the voltage under load.
It is built around an adjustable current sink with a range of 10 uA to 200 mA, controlled by a small ARM Cortex processor that also handles the rotary encoder input and LCD output.
The battery holder is a "BF-2A", found on Banggood. Henrik Jensen (forum user HKJ) put me on to it.
![Show the homemade equipment you are using now.](https://www.eevblog.com/forum/index.php?action=dlattach;topic=152600.0;attach=1843687;image)