Last time, I diagnosed a junk Makita battery using the BTC04. This time, I'll connect it to a computer to diagnose and repair it.

Last time, I used the Makita genuine battery checker "BTC04," which costs about 27,000 yen, to check the condition of nine junk batteries.

This time, instead of using the BTC04, I'll use an Arduino Nano to communicate between the battery and the computer.

The components used are relatively few:
Arduino Nano (with ATmega328)
4.7kΩ resistors × 2
Battery communication terminal

I'll make a simple communication adapter and use Open Battery Information (OBI) to read the information recorded inside the Makita battery.

From the computer, I can see quite detailed information, such as:
Battery model number
Charge count
Battery status
Battery voltage
Voltage per cell
Temperature sensor value
Manufacturing date
Fault description


Furthermore, since some batteries allow for "error clearing" and "battery message resetting," I'll try clearing the errors on the junk batteries.

And... amazingly, the fault indicator disappeared and they started charging normally!

Did the batteries truly recover?

I'll also compare the diagnostic results from the Makita genuine BTC04 used last time with the data read from the computer to see how closely they match.

Furthermore, examining each of the nine junk batteries individually revealed different conditions, such as batteries with apparent temperature sensor malfunctions and batteries unable to communicate at all.

This is only a partial verification; in the future, I plan to further disassemble the batteries to check the actual cell voltage and internal condition.

Microcontroller Board
Items Used
3 x NANO V3.0 CH340 (Solder Pins)
https://amzn.to/46JXPsd

Recommended Items
2 x NANO V3.0 CH340 (Unsoldered Pinouts)
https://amzn.to/4heaSYX
3 x NANO V3.0 CH340 (Unsoldered Pinouts)
https://link.amazon/B0hh8ajYn

Resistors
Carbon Resistor 1/4W 5% 4.7kΩ
Kyoritsu Electronics (Cheaper than Amazon, even with shipping)
https://eleshop.jp/shop/g/g6AY315/
Amazon
https://link.amazon/B09XYexdD

Communication Connector
https://amzn.to/4yeFhfL

Open Battery Information Website
　https://openbatteryinformation.github...

Temperature sensor replacement video
　赤点滅で充電出来ないマキタの18Vバッテリーを修理するよ！

Previous video
　マキタのジャンクバッテリー9個をBTC04で診断したら、驚きの結果に… #0184

*Regarding the problem of not being able to write the firmware

The video shows operation on Windows 11 + Chrome without any special settings.

Is the microcontroller board recognized by the PC?

If not, there may be a problem with the USB cable or the microcontroller board.

The video below shows how to check the communication status between the PC and the microcontroller board.

Repairing a junk Makita battery for 25 yen! The device was revived after replacing the temperature sensor #0186

マキタのジャンクバッテリーを25円で修理！温度センサー交換で復活した #0186
Also, please check if your security software or other programs are interfering.