Introduction: Lithium Battery MAh Tester

Bought some expensive battery you want to test, or just have old one lying around youre interested in playing with?

its the project for you!

its the simplest tester you can make for only about $10, and for that price youll get to make astonishing graph.

[ITEM] youll need:

  • Arduino (2$)
  • Relay module (2$)
  • RTC DS3231 (2$)
  • MicroSD module +SDcard (2$)
  • a hand full of wire
  • 2LEDs (red and green) + 2X 1KOhm resistor
  • Button
  • LM317 (1$)
  • 1-1.2Ohm resistor 5Watt (1$)


  • auto cut-off @ 3v
  • green LED when discharging/testing
  • red LED when OFF
  • Data Logging on microSD card
  • 1.2Ah discharge with 1Ohm resistor (can be changed)

Step 1: Constant Current Regulator

you'll need a constant current load, easy enought when you have the circuit diagram!

i didnt put the capacitor on mine, it works good enought as is.

you'll obviosly need to look for the pinout.


find yourself an old pc and rip the chipset heatsink out of it. drill and tap you are good to go!

it will dissipate aprox 5W with a 1Ohm resistor at about 1.2Amp discha

Step 2: Shape the Data

your data will look like this:


use anything to shape it like this:


am using notepad++, go to macro->record->use to bottom of page

rename the .txt to .csv


you'll just need to input the .csv into a graph generator like datplot

DS3231 lib: