How PackGauge started
It started with a simple question
from my dad.
My dad noticed that the battery packs for his cordless mower would indicate a full charge while on the charger, but after removing them and pressing the battery’s fuel-gauge button, they would sometimes show only three bars instead of four. He asked me what might cause that.
Why should I need a laptop every time I want to check a battery?
What started as a simple question about one of my dad’s batteries became PackGauge — a standalone tool built to make battery health easier to see, understand, and share, without opening the pack or connecting it to a computer.
Read the full build story
I started researching how the packs worked and learned more about the individual cell groups inside them and how differences in their voltages can affect the overall health and performance of a battery pack. The problem was that checking those voltages normally meant opening the pack and measuring each group individually — something I wanted to avoid.
While researching, I came across an open-source battery communication project by mnh-jansson and its contributors. I was amazed by how much information they had been able to decode directly from the battery’s communication interface. Suddenly, it looked possible to see the individual cell-group voltages and other useful battery data without opening the pack at all.
I started looking for a small standalone platform and found the inexpensive ESP32-based display commonly known as the Cheap Yellow Display. It already combined a touchscreen, an ESP32 microcontroller, Wi-Fi, and Bluetooth in one compact package. It was more than capable of what I originally had in mind — and opened the door to doing quite a bit more.
The idea grew from simply displaying cell voltages into a handheld battery diagnostic tool that can show cell imbalance, charging and tool-use history, fault counters, current-load and condition charts, save scans, and send results over Wi-Fi.
With the hardware selected and the battery communication work provided by the open-source community as a foundation, I began developing PackGauge with the help of ChatGPT and Claude.