YOU CAN BUILD A READER THAT TELLS YOU WHY A DEAD POWER TOOL BATTERY IS NOT ACTUALLY DEAD
A reader that tells you why a dead power tool battery is not actually dead — and sometimes lets you bring it back.
WorkshopOpen-hardware
- difficulty
- ●●●○○
- time
- a weekend
- license
- NOASSERTION
- repo
- repo ACTIVE50 stars
●●●○○ · a weekend · NOASSERTION · 50 stars · repo ACTIVE
WHAT YOU’LL NEED
- Electronic parts — full list with part numbers in the repo BOM
- Dev board / microcontroller — runs the project firmware
Partner
COMPAREE VERDICT
PocketOBI is a handheld diagnostic tool for Makita LXT 18V battery packs, built on an ESP32-C3 with a small TFT screen and a rotary encoder. It speaks the OneWire protocol that the Open Battery Information project reverse-engineered, so it can read what the pack is actually reporting: per-cell voltages with colour-coded health and imbalance, both temperature sensors, charge count, manufacturing date, model, and error state. It can also clear a false lockout. The repository publishes firmware and a full parts list, and the project is actively maintained. What it does NOT publish is an enclosure or PCB — you are building this on breadboard or a generic prototyping board, and the README assumes you know how to wire an ESP32 to a display and a rotary encoder. The single biggest trap is not the build, it is the safety: these packs hold lithium cells and up to roughly 21 volts, the ESP32 must never touch the pack's positive terminal, and a pack with a genuinely bad cell must not be forced back into service because that is a fire risk. The project carries no licence file, so commercial use is legally unclear. For someone who repairs Makita packs and wants to see what the BMS is actually saying, this is exactly the tool. For someone unfamiliar with lithium pack safety or ESP32 wiring, this is a weekend that could go very wrong.
IN THE REPO
NOT IN THE REPO
- —Firmware is published and actively maintained, built on PlatformIO for ESP32-C3
- —Full bill of materials is in the README with vendor links to AliExpress and Amazon
- —No enclosure files or 3D models — you are building this on breadboard or solderable prototyping board
- —No licence file in the repository; README says NOASSERTION, so legal status for commercial use is unclear
- —This is beta software with a blunt safety warning: lithium cells, up to 21V, never connect the ESP32 to the pack's B+ terminal
- —The project can reset a false BMS lockout, but forcing a pack with a genuinely bad cell back into service is a fire risk
Can I build this?
Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.
Partner · KickstarterHeyGears G1: 10M+ colors and transparent parts in one print, plus UV printing on flat objects. Figures, parts and labels — no painting.
Videos
PocketOBI - Makita Battery Diagnostic Tool5:37
Build walkthrough and demonstration by The Repair Forge, showing the display interface and a real diagnostic of a pack with a failed thermistor
Gallery
Start here
Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.
- 1.Read the safety section in the README (This is not optional — the project works with live lithium cells and up to 21V, and the wrong connection can damage the ESP32 or worse)
- 2.Order the parts from the bill of materials (README links to AliExpress and Amazon; the core parts are an ESP32-C3, a 1.3-inch ST7789 TFT, and a rotary encoder)
- 3.Wire the ESP32 to the display and encoder following the pinout in the README (The project assumes you know how to connect an SPI display and a rotary encoder; if this is your first ESP32 display project, find a basic ST7789 tutorial first)
- 4.Flash the firmware with PlatformIO (The README gives PlatformIO instructions; Arduino IDE is also supported but PlatformIO is the documented path)
Resources
Documentation, files and community threads for this build — we link straight to the original sources and never rehost the creator’s files.
KNOWN ISSUES
- The repository publishes no enclosure, no PCB, and no wiring diagram beyond a text pinout — you are expected to wire this yourself on breadboard or a generic prototyping board
- The ESP32 must never be connected to the battery pack's positive terminal (B+); the README is explicit about this, but it is the single most dangerous wiring mistake
- The project can clear a false BMS lockout, but forcing a pack with a genuinely bad cell back into service is a fire risk — the tool shows you the data, but the decision is yours
- Replacing a faulty thermistor inside a Makita pack requires opening the case and working around live lithium cells; if you have never opened a lithium pack before, this is not the project to learn on
- The repository carries no licence file (README says NOASSERTION), so commercial use or derivative projects are legally unclear
- The OneWire protocol is Makita LXT-specific — this will not work with other brands' battery systems
Does this work with other battery brands?
No. The OneWire protocol is specific to Makita LXT packs. Other brands use different communication protocols, and this tool will not read them.
Can I use this to revive any dead battery?
No. It can clear a false BMS lockout if the cells are genuinely healthy, but a pack with a bad cell must not be forced back into service. The tool shows you the data; you still have to make the safe decision.
Do I need to build a custom PCB?
No PCB files are published. The project is designed to be built on breadboard or a generic prototyping board, wired according to the pinout in the README.
What is the most common cause of a false lockout?
Failed thermistors. In the documented case in the README, one sensor reported -30°C while the other read 28°C, so the charger refused to start. The cells were fine; the thermistor cost about twenty cents.
Community builds
No community builds yet — be the first, we feature the best ones.
Discussion1
FROM THE COMPAREE TEAM
147 stars, beta software, and a blunt safety warning about lithium cells and 21V — but it tells you what a $100 Makita pack is actually reporting, which no charger will. Have you ever binned a pack that turned out to be a twenty-cent thermistor?
The Repair Forge
The Repair Forge built PocketOBI to diagnose Makita LXT battery packs without a computer, using the OneWire protocol that the Open Battery Information project reverse-engineered. The project is maintained on GitHub and documented on YouTube.
Keep building — related projects
Same category, picked by how close they are to this build.
FULL CADA tiny homemade board makes one keyboard and mouse flow between two computers
Open-hardwareWorkshop●●●○○moderate
FULL CADThis open-source robot places 30 chips a minute - and you can build it yourself
Open-hardwareWorkshop●●●●●expert
Partner · KickstarterCodeeBot: build the robot from Lego-compatible bricks and program it by hand; a GPT tutor explains each step.
FULL CADYou can build a soldering station that runs off a USB-C laptop charger
WorkshopOpen-hardware●●●●○advanced
NO CAD FILESFree software turns your drawing into embroidery — the only cost is the machine
WorkshopOpen-hardware●●●○○moderate
DISCLAIMER
- Comparee is not the author of the projects featured here. All rights to each project belong to its creator — every page links to the original source, and we never host creators’ files.
- Information is provided without warranty and may become outdated as projects evolve. Prices are indicative bands only — always check the creator’s parts list for current costs.
- Building and operating any project is at your own responsibility. Protective equipment, safe workshop practice and compliance with local regulations are the builder’s responsibility.
CompareeTEAM11d ago
Practical notes from our verification: the YouTube walkthrough (Fxc9aUqT9bo) is by the project creator and is the clearest guide to the interface and wiring. The repository moved under TheRepairforge organization and is actively maintained. The documented thermistor failure case is real and detailed in the README. The single biggest upgrade path is not the hardware — it is learning to safely probe a lithium pack before you connect anything, because the ESP32-to-B+ mistake is instant and permanent.