The Repair Forge The Repair Forge

A Makita battery tester you build yourself.

Reads Makita LXT 18 V batteries, gives one verdict, and clears false lockouts. An ESP32, a screen and a knob. No PC.

Build guide Flash the firmware
PocketOBI home screen: Battery, Repair, Tools, About

Pick a board

The kit laid out: carrier PCB, ESP32-C3 SuperMini, screen and encoder module, battery adapter lead, resistors, terminal block and the printed case

ESP32-C3 on the carrier PCB

The reference build. A rotary knob and a back button, a two-layer board with a handful of hand-solderable parts. Fabricated and bench-validated.

Build guide and the printed case on Printables

The CYD board, back side, with the CN1 connector marked

CYD (ESP32-2432S028R)

The "Cheap Yellow Display": same firmware, a touch screen, less soldering. Boards vary between batches, so check yours against the notes first.

CYD guide

The ES3C28P board, back side, with the Expand, I2C, UART and BAT sockets labelled

ES3C28P (ESP32-S3)

A 2.8" ESP32-S3 board with a capacitive touch screen. Same firmware as the CYD. It has a LiPo charger on board, but running it from a cell instead of USB is not tested yet.

ES3C28P guide · Board render: LCDWiki

Flash the firmware

Plug the board in with a data USB cable, pick your board, click Install.

This browser can't flash a board: use Chrome or Edge on a computer. Flashing needs a secure (https) page.

Asia firmware, English with Japanese, Korean, Vietnamese and Chinese (日本語, 한국어, Tiếng Việt, 中文): ESP32-C3ESP32-C3 or CYDCYD. The other builds carry English, French, German and Spanish; the ES3C28P build adds Vietnamese.

Works in Chrome and Edge on a computer. Anywhere else, download the firmware from the latest release and flash it with esptool, or build it from source.

Firmware licensed PolyForm Noncommercial 1.0.0. Third-party components.

If it doesn't go as planned

  • Board not detected. On the ESP32-C3, hold BOOT while plugging it in. On Windows the CYD may need the CH340 USB driver. The ES3C28P needs no driver; if it is not seen, hold BOOT, press RESET, then release BOOT.
  • Mirrored image on the CYD (text reads right to left, the title bar looks olive green). Some CYDs have an ILI9341 screen: install the cyd-ili9341 file from the releasethe cyd-ili9341 file from the release instead, then run Settings > Calibrate touch once. Details in the CYD guide.
  • Erase device wipes the saved language and the touch calibration. Leave it unticked for an update.
  • Which version is on it? The About screen shows it.
Your makita battery remembers everything you did to it! The tool screen by screen, then the whole build: parts, PCB, assembly, firmware.

Everything else is on GitHub

The source, the hardware files, the release notes and the full documentation live in the repository.

PocketOBI on GitHub

Next: read your packs on a PC with PackScope.