What it is

PocketOBI is a small standalone reader and diagnostic tool for Makita LXT (18 V) battery packs: a screen and a rotary knob, no PC needed. It shows the cell voltages, temperatures, charge count and lock state of a pack, gives a traffic-light verdict, and can clear a BMS lockout when it is a false positive, typically after a cell was slightly over-discharged, so that still-good packs do not get thrown away.

The honest limit: a pack with a real fault locks again, and the tool says so instead of pretending.

This is the carrier PCB: a 2-layer, 91 x 34.5 mm board that sockets an ESP32-C3 SuperMini and a 2.4" ST7789 TFT + EC11 encoder module, carries the two pull-up resistors and breaks out the battery connector. Everything is through-hole and easy to hand-solder. These are the exact Gerbers I ordered and validated on the bench (v1.0 rev A, 2026-08).

Ordering

Click Add to cart on this page: the board settings are already filled in. The defaults are fine: 2 layers, FR-4, 1.6 mm, HASL, any solder mask colour. No controlled impedance, no special stackup. Quantity 5 is the cheapest.

Parts

• U1: ESP32-C3 SuperMini (any ESP32-C3 board with native USB, same footprint)
• M1: 2.4" ST7789 TFT + EC11 rotary encoder 2-in-1 module (12-pin header), on a 1x12 2.54 mm female socket
• Battery_Interface1: JST-PH 6-pin vertical header (B6B-PH-K), to the Makita LXT battery adapter
• Battery_GND1: 2-pin screw terminal, 3.5 mm pitch (battery B-)
• R1, R2: 470 ohm through-hole resistors (DATA and ENABLE pull-ups)
• A Makita LXT battery adapter (the kind with the orange connector) to reach the pack terminals

Socket both modules on female headers so they stay removable.

Wiring and safety

Never connect the battery B+ (up to ~21 V) to the ESP32. The board does not route B+ at all: only DATA, ENABLE and GND (from the B- terminal) come from the pack. Wiring, pinout and the adapter's connector numbering are in the hardware notes: HARDWARE.md.

Firmware

Flash it from the browser, no toolchain needed: therepairforge.github.io/pocketobi. Source, releases and changelog: github.com/TheRepairforge/PocketOBI. The UI is in English, French, German, Spanish, and an Asia build adds Japanese, Korean, Vietnamese and Chinese. PocketOBI also works as a USB adapter for a PC app (PackScope).

Enclosure

The 3D-printable enclosure is on Printables: PocketOBI - Makita 18V LXT Battery Diagnostic Tool.

See it working

Walkthrough on YouTube: https://youtu.be/8Qe2dTXrJ8g. Channel: The Repair Forge.

Credits and licence

PocketOBI speaks the Makita OneWire protocol documented by the open-source Open Battery Information project (Martin Jansson, MIT). The board files are licensed CC BY-NC-SA 4.0; the firmware is PolyForm Noncommercial 1.0.0.

Lithium packs store a lot of energy. Clearing a lockout only helps a pack whose cells are actually healthy; do not force a pack with a genuinely bad cell back into service. Use at your own risk.