The other day I put one of my Milwaukee M13 batteries to charge like I always do, but this time it just did not start charging.
Normally, when I put the battery to charge, it shows a solid red or green light depending on the charging; but this time, both the lights started flashing and the battery did not charge at all.
I figured something was off so I looked up online and found out that it’s a common issue with older M12 batteries.
I also made a short YouTube video about this topic which you can watch below before you continue reading this article.
On the video, I showed the 3 different ways you can reset a Milwaukee M12 battery: using another healthy Milwaukee M12 battery, a battery from another brand with similar voltage, and a DC power supply.
How to Reset Milwaukee M12 Battery in 3 Different Methods
I decided to try a few reset methods to see if I can bring it back to life, follow along if you are facing the same problem with your M12 batteries.
Try resetting using another battery
The first method I decided to try was something I read about a few times, it’s basically using another good condition Milwaukee battery to “jump” the dead one.
I started by checking both the older battery and the fresh battery using a multimeter, the healthy battery showed the voltage of almost 12V which is perfect, but the one that wasn’t charging was stuck around 10V, which confirmed it was under voltage.
So I identified the positive (C3+) and the negative (C1-) terminals of both the batteries and connected positives and negatives together using jumper wires.
After setting up the connection, I let the batteries sit for like 15 seconds to allow the charge to transfer and jump start the dead battery.
Next, I disconnected the wires and popped the old battery back into the charger and it started charging normally. No flashing red and green lights, only a solid red light like it should be when the battery is charging.
Resetting using battery from another brand
The first method worked out for me, but if it didn’t for you, I found this trick that might help; jump starting the battery using a 12V battery from a different brand.
I had an old Makita battery lying around from an old drill I haven’t used in a while, so I figured I’d give it a shot too.
Just like before I identified the C3+ and C1- terminals on the Makita battery and connected them to the Milwaukee battery using jump wires, positive to positive and negative to negative.
I left the batteries connected like that for 15 seconds and that little push was enough for the Milwaukee battery to wake up and start charging normally again.
So yes, even if you don’t have another Milwaukee battery, something like an old battery from another company can also do that trick as long it’s 12V and you connect the terminals correctly.
Using a DC power supply
If neither of the battery methods work for you, another option to try that I also use is using a DC power supply to manually bring up the voltage to reset the battery.
I set my DC supply to 12V and current to 1A to match it with the Milwaukee battery.
Then I grabbed a pair of jumper wires and connected them to the battery on one end and used a clip jump wire connected to the DC power supply on the other end, C3+ to C3+ and C1- to C1-.
Make sure the connection is secure and let the current flow for about 15 to 20 seconds, allowing the battery to take charge and jump start. Once that was done, I switched off the power supply and disconnected the wires.
Insert the batteries back into the charger and the battery should be charging again, If it still shows flashing lights, don’t lose hope, it did for me too at first, it takes a few times to register the battery, just try replugging it 1 to 2 times and that should reset the batteries.
And before I end this article, I’ll share to you another short video I’ve made about the different meanings of the indicator lights on a Milwaukee M12 battery charger. This is very important so you’ll know if there’s something wrong on your battery or not. You can watch the video below.
A solid red means the battery is charging and this will turn into a solid green once the battery becomes fully charged. A flashing red and green indicates a bad battery while a flashing red only means a hot/cold delay.
