Battery capacity tester: with this device you can check the 18650 battery, acid and other (the biggest battery I tested It’s 6v Acid battery 4,2A), I need It to check fake china battery.
For safety, I added, using a thermistor, the temperature of the power resistance and battery to prevent going too hot, with this trick I can check 6v Acid Battery without fire the board.I
I select little micro controller atmega328 compatible nano (eBay).
All the code is here.”

Link