Anyone got a clean pinout for the Milwaukee M12 battery?

[Thomas Martinez]

Been digging around to find a solid reference for the pinout of the M12 packs. From what I can find online, it's C1- to negative, C3+ as the positive, the T line go to a thermistor to monitor the temperature of the pack, and C1+ and C2+ are the balance pins for each cell group.
Given the number of cells in the pack, it makes sense that these balance pins would be along each group of cells. It seems like there's some debate about whether the charger or the pack itself performs the balancing function, though. I haven't scoped the thermistor on any Milwaukee M12 packs yet to find the value of the thermistor that they use. Does the tool check the thermistor on the pack itself? Also, are the balance pins always live, or only if there's a pack docked to the tool? Has anyone rebuilt any of these packs? If so, did they have to take any special steps to reattach the balance leads? There doesnt seem to be much documentation on how these M12 packs work outside of the tool's documentation, so figured it was worth a thread.

 

[Biblical Chicken]

your pinout is right. The charger does balancing not the pack, the M12 packs are dumb, no real BMS just protection.

 

[Crazy Crane]

scoped out the thermistor on a gen 2 pack, its a 10k NTC. Tool checks it, fried thermistor line on one pack and tool would not spin up despite fine voltage reading.

 

[Misty Mandrill]

your pinout is right. The charger does balancing not the pack, the M12 packs are dumb, no real BMS just protection.

wait so if the charger does the balancing what happens if I only run the pack on the tool and never charge it past 80%?

 

[Biblical Chicken]

wait so if the charger does the balancing what happens if I only run the pack on the tool and never charge it past 80%?

basically yes. That's why people get one weak cell group on their M12s because the charger never balances the cells if they're never charged to 100%. You have to use them flat to full once in a while to balance them out.

 

[Gorgeous Gerbil]

M12 packs are garbage anyway, m18 all day

 

[Escape from the Scooter J]

your pinout is right. The charger does balancing not the pack, the M12 packs are dumb, no real BMS just protection.

You have to include in that there is a small BMS on the pack that cuts out if the cells are over discharged or overvoltage during charging. It's not for balancing but the "dumb" of the M12s undersells it. The taps go to the BMS itself. There is no balancing done on the tool, it just read the cells voltage to report to the user.

 

[Divine Worm Ma]

rebuild a 4ah m12 last summer. Pulled three samsung 18650s out and replaced with three fresh new ones. Kept the original pcb on the pack. M12 came back fine but had to charge to 100% for the charger to stop blinking red on me. Did some spot welding on the balance leads and got them back to their original tabs on the PCB.

 

[Misty Mandrill]

rebuild a 4ah m12 last summer. Pulled three samsung 18650s out and replaced with three fresh new ones. Kept the original pcb on the pack. M12 came back fine but had to charge to 100% for the charger to stop blinking red on me. Did some spot welding on the balance leads and got th…

interesting so if I were to do a pack rebuild with fresh cells would the Milwaukee charger just sort out the cells on its own or would I have to get them all to the same voltage with a hobby charger first?

 

[Divine Worm Ma]

interesting so if I were to do a pack rebuild with fresh cells would the Milwaukee charger just sort out the cells on its own or would I have to get them all to the same voltage with a hobby charger first?

bring them to the same voltage first. Milwaukee chargers will not compensate for significant difference in voltage between cells. It will throw a fault and refuse to charge. Charge each group to 3.7v with my imax b6 before reassembly.