“Ever wondered if your batteries are any good? I built a tester with data logging and tested every battery I could get my hands on.
It all started with a set of seemingly bad NiMh batteries and the desire to know if they really are that bad. From that point it kinda escalated. I built the Battery Analyzer and its successor the MkII and started testing NiMh batteries. When the NiMh tests entered their long and boring last phase, the long time self discharge test, I started testing Alkaline batteries. Initially I only intended to test the offering of my main supermarket, but I just couldn’t stop. I ended up testing 25 types of Alkaline and two types of LiFeS2 batteries.
The Hardware:
While the first Battery Analyzer did its job I wasn’t quite happy about the fixed load resistors. I took the chance to learn how to design my own PCB and created the MkII with a programmable constant current load. Like the MkI it is designed as a hat for the Arduino Mega 2560, which might not be as fancy as a standalone device, but for my first PCB I didn’t want to bite off more than I could chew. The measurements are done by an Adafruit INA219 module and the constant current load consists of a MCP4725 12-Bit DAC, a TLV2372 rail-to-rail OpAmp and an IRLZ44 MOSFET (as well as some caps and resistors). Additionally it uses a generic 0.96” 128x64 OLED display and a micro SD card adapter.
When the Battery Analyzer gets powered on the OLED display shows a selection menu for Alkaline, NiMh and LiPo/Li-Ion batteries. This selection determines the test end voltage. The next screen shows the discharge current selection. If OK is pressed the test starts. First a battery check is performed to see if it is already discharged, missing or in reverse. If everything’s OK the CC control sets the discharge current and the INA219 takes a measurement every second which is then displayed on the OLED screen. Every 15 seconds a data point is logged to the SD card in CSV format. If the SD card is missing the optional logging is disabled and a message is displayed on the screen. The test ends when the battery reaches the end voltage and a message will be shown.”