As a Milwaukee tool lover, I own both of the M12 and M18 milwaukee tool.
While M18 is powerful enough for most of the task, sometimes I just want to use a tool for light task like screwing, etc.
Hence, M18 a bit over powered and M12 is indeed a great choice in this case.
I own several M12 battery and I opened up the cover to check pinout of the milwaukee M12 battery.
There are 5 pins on the PCB of the M12 battery, namely as below:
C1- is Negative terminal
C3+ is Positive terminal (This is the overall positive terminal, not junction between any battery cell)
T is Thermistor, used for temperature monitoring
C1+ and C2+ is junction between cell groups (There are three pieces of 18650 battery, must charge every cell in balance)
Milwaukee M12 Battery Interface & Pinout Wiring Diagram
After checking the voltage and resistance value of each pin, I draw the pinout diagram of this Milwaukee M12 battery.
This 12V battery from Milwaukee is quite simple compared to other 18V or 20V battery like Worx 20V or Porter-Cable 20V battery.
I used a digital multimer to measure the voltage and resistance.
Here are the data:
Data Measured from Milwaukee M12 (12V) Battery
C3+ and C1- = 12V (Between positive and negative terminal)
T and C1- = 0V
T and C3+ = 0V
C1- and C1+ = 4V (One cell)
C1- and C2+ = 8V (Two cells)
C1- and C3+ = 12V (Three cells)
C1- and T = 10 kΩ (25 °C), ~8KΩ (Current Temp) – I believe it use a thermistor that would have 10 kΩ at 25 °C. During my measuring, it shows only around 8KΩ due to my room temperature. Thermistor resistance value changes with temperature to prevent the tool being used or charged when it is overheat or too cold.
C3+ and T = 0Ω
The image above show a 3.0Ah milwaukee m12 battery.
If it has higher capacity, it could have different shape (Similar to the Ryobi 18V battery shape, but just smaller in size)
If you want to know more about your m12 battery, use phone to scan the QR code and check its information.
As mentioned before, there are 5 pins, namely +, -, C1+, C2+ and T.
Each pin has its own function.
Yes, “theoretically” you should only charge the battery with the original milwaukee M12 charger.
Side by side comparison when the battery case is removed.
If you are interested to know more the battery management system, you could try to reverse engineer every components on the PCB board above.
As mentioned, it uses 3 pieces of high quality 18650 battery, connected in series to give an output of 12V.
This is the close view of how these 18650 battery cells being connected.
