Balance your Milwaukee M12 batteries!

400bird

Solar Wizard
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May 23, 2020
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I've got about 7 Milwaukee M12 batteries. This morning, one 6.0ah battery failed to charge and the charger started blinking alternating red and green LEDs. The symbol on the charger reminds me of a broken heart, but a battery instead of a heart. You can see the led key on the charger below.

I decided to get some voltage readings and found a 0.7 volt delta between the cells.
C1 = 3.7 volts
C2 = 3.0 volts
C3 = 3.65 volts

Well, I've got a iCharger X8, I can fix that!
Then I realized I also have an M12 charger that I never use. So ummm, tada!?

1698039017915.png+
Ugh, that pic sucks, but you get the point. Balance charger bodged into a real Milwaukee socket. The Milwaukee charger still has the 120vac plug, so it should work, but here it isn't plugged into the wall and is mostly just providing a connection point for the balance charger.

That first pack balanced nice and slow over a few hours while I was doing something else. I unplugged it before it finished to go make dinner.
After dinner, I decided to check the balance on all the other packs.

1698039135720.png

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1698039161710.png

1698039174378.png

1698039191119.png

1698039220169.png

And I think this was the best pack. Guess what's going to be sitting on the table in the office balancing cells all day tomorrow?
1698039207083.png

Anyways, it sure does seem like Milwaukee M12 batteries don't do any cell balancing.
Just out of curiosity, I opened a single M18 battery, the cells were 3.886-3.889 volts, so a much better BMS in the M18.
 
I've had a couple m12 batteries give me the error like that. One charged ok on another charger but one 2.0 i have won't charge on any charger. Now I see what the problem is. I did plug it straight to a 12 volt battery and it charged up but I know that's not safe or practical to keep doing.
James
 
This is awesome, thank you! I have an M18 8ah HO that's been giving my issues with extremely low capacity and quick charging but no errors. I also have a pile of M12. Time to order one of these balancers...
 
Ok...
Now you have to show how you "modded" the balancer into the charger.

The 6.0 packs are 2p3s, and FRAGILE I have several that are unchargable.
I am looking forward to your description!
 
Ah, thanks for this. Was considering my next cordless tool to be a Milwaukee one (and I might still do that) but looks like I need to better research how the batteries hold up over time in the different brands Dewalt/Milwaukee/Makita/Ryobi/harborfreight/etc. And do batteries tend to last longer when they are cycled every day or week vs. those that are only cycled a few times a year.

In any case, cool that you found a solution, though it's one I hope I could avoid by buying once, crying once (or buy the right model of a budget brand, aka M18 vs M12).
 
Ah, thanks for this. Was considering my next cordless tool to be a Milwaukee one (and I might still do that) but looks like I need to better research how the batteries hold up over time in the different brands Dewalt/Milwaukee/Makita/Ryobi/harborfreight/etc. And do batteries tend to last longer when they are cycled every day or week vs. those that are only cycled a few times a year.

In any case, cool that you found a solution, though it's one I hope I could avoid by buying once, crying once (or buy the right model of a budget brand, aka M18 vs M12).
I have used MKE exclusively for my business for the last 10 years... I still have many original m12 Batts, my brother ALSO uses them, so I'm frequently missing batteries.
They are very long lasting sets.
 
I have used MKE exclusively for my business for the last 10 years... I still have many original m12 Batts, my brother ALSO uses them, so I'm frequently missing batteries.
They are very long lasting sets.
I started with Bosch around 10 years ago, I saw what Milwaukee goes through at work in an industrial setting and was blown away... I started buying red around 5 years ago, Fuel version ftw, and I'll never look back.
I've been impressed with my M12 and feel it would be more than enough for most people but my M18 still gets used heavily as well.
 
I'm still loving all my M12 tools and the one battery is the only one that does anything unusual.
There's a chance this battery is the one that fell from the roof ?

Ok...
Now you have to show how you "modded" the balancer into the charger.
You want to see my soldering ?
I Guess I can open it back up and grab some pics. The terminals on top of the battery are labeled +, -, C1, C2, and I think T
I'm just soldered to the 4 connections needed to grab all 4 test points. (Not T)
The 6.0 packs are 2p3s, and FRAGILE I have several that are unchargable.
I am looking forward to your description!
My 4.0ah packs are also 2p3s they're all still working
 
I don't know if this is the same things, but my wife has the heated jacket that takes those batteries. Our last one, it would drain all the way down and then wouldn't take a charge anymore. We had to "jump start" it with a 9v battery for 1 minute then the charger would recognize it and start charging.
 
I don't know if this is the same things, but my wife has the heated jacket that takes those batteries. Our last one, it would drain all the way down and then wouldn't take a charge anymore. We had to "jump start" it with a 9v battery for 1 minute then the charger would recognize it and start charging.
Absolutely…
The jacket drains them down so slowly, it doesn’t trip the BMS safety.
Unless ya run on red. Blue or white, and it just drains them down.
ESPECIALLY if you are only running the pocket warm.
 
Milwaukee forever here !

I haven't had any battery issues so far but I'm interested in this to keep them in good shape.
 
I've been running Milwaukee tools for 5 years now. I've only had the problem with one m12 battery and it was a infrequently used one. In the 5 years I've been using them I haven't replaced any M18 batteries or wore out any of the tools. I've had my M18 1/2 drive impact so hot I couldn't touch the nose cone while changing sprockets on a D8 dozer and it never slowed down!
 
Oh, I have obliterated MANY of the tools...
I USE them.
I have destroyed several impact drivers. Several impact drills, fans, shop vacs, etc... many still during the 5 year warranty, and gotten replacements...
But they WORK! And I will always replace them.
 
Any balancing success?

Wondering because there's a 1k resistor between the cell level wire leads and the per cell top terminals.
 
I have the older M28 volt Milwaukee sets that I have had for 20 years. One of the original batteries is still holding a charge and I have picked up two of the newer generation batteries. Great tools and battery life despite lots of use and abuse. They are clunkier than the new style tools with the ECM brushless motors but hard to switch over when they still run and do what I need them to do
 
Ah, thanks for this. Was considering my next cordless tool to be a Milwaukee one (and I might still do that) but looks like I need to better research how the batteries hold up over time in the different brands Dewalt/Milwaukee/Makita/Ryobi/harborfreight/etc. And do batteries tend to last longer when they are cycled every day or week vs. those that are only cycled a few times a year.

In any case, cool that you found a solution, though it's one I hope I could avoid by buying once, crying once (or buy the right model of a budget brand, aka M18 vs M12).
Re: brands of batteries

I have some original 3.0Ah Makita LXT batteries that came with my first Makita LXT kit from a decade ago. They still charge and still work. They're definitely aged as runtime isn't as long as it used to be, and I think it has impacted the max amps output as well (the circular saw bogs down more on the old freshly charged battery than it does on the half-drained one year old battery for example). But I think getting 10+ years out of cordless tool battery packs is pretty darn good. I didn't treat them with kid gloves either.

At the time I bought them, it seemed Milwaukee, while seeming making good stuff, kinda had this cult-like following and the price tag to match. Wasn't sure if it was worth the price, and I tend to avoid cult-like followings (I was probably the only college kid without an iPod back in the day), so I shopped around some more and settled on Makita. Never regretted it. I have several tools from them now and it is great to use the same batteries in my impact driver, saw, 1/2" impact, and weed eater.
 
Great thread!!! I was just wondering yesterday if my M12 batteries only get balanced if you fully charge. I purposely try not to fully charge them unless im about to use it that second.
Im going to copy your trick. But instead of fully charging i will just pick a number like 3.8v and probe each cell individually. I dont have a spare M12 charger to modify. Ive got an older Icharger 308duo that should work.
This time of year i keep a thermoelectric cooler in my truck just to keep my batteries from suffering inside truck temps. My 12.0aH M18 lives in the fridge at home because i rarely need it.
Im pretty surprised how far outta whack the OP cells are. I measured mine from the factory out of curiosity. Forget the numbers but i wasnt all that impressed by voltage differences.
I know there is that ONE KEY tech. Have milwaukee chargers gotten smarter over the years? I have a M12/M18 rapid charger bought about 4 months ago. I wonder if that balances the cells better because it might have a newer bms? I keep meaning to measure its output with different size batteries. I dont want to give my little 2.0aH batteries the same current as a larger battery. So i rarely use the rapid charger. Yesterday was the first time i put an M12 battery on it. The 2.0ah sure felt warm and only left it on for 10 minutes.
 
Any balancing success?

Wondering because there's a 1k resistor between the cell level wire leads and the per cell top terminals.
I was wondering why it's going slow as mud. I'm something like 20 hours into one battery.
I was waiting to post results once I was a bit further along
 
Interesting info. Now you have me wanting to look into the BMS's in my m12, m18, and EGO batteries.
 
I've got about 7 Milwaukee M12 batteries. This morning, one 6.0ah battery failed to charge and the charger started blinking alternating red and green LEDs. The symbol on the charger reminds me of a broken heart, but a battery instead of a heart. You can see the led key on the charger below.

I decided to get some voltage readings and found a 0.7 volt delta between the cells.
C1 = 3.7 volts
C2 = 3.0 volts
C3 = 3.65 volts

Well, I've got a iCharger X8, I can fix that!
Then I realized I also have an M12 charger that I never use. So ummm, tada!?

View attachment 173690+
Ugh, that pic sucks, but you get the point. Balance charger bodged into a real Milwaukee socket. The Milwaukee charger still has the 120vac plug, so it should work, but here it isn't plugged into the wall and is mostly just providing a connection point for the balance charger.

That first pack balanced nice and slow over a few hours while I was doing something else. I unplugged it before it finished to go make dinner.
After dinner, I decided to check the balance on all the other packs.

View attachment 173691

View attachment 173692

View attachment 173693

View attachment 173694

View attachment 173695

View attachment 173697

And I think this was the best pack. Guess what's going to be sitting on the table in the office balancing cells all day tomorrow?
View attachment 173696

Anyways, it sure does seem like Milwaukee M12 batteries don't do any cell balancing.
Just out of curiosity, I opened a single M18 battery, the cells were 3.886-3.889 volts, so a much better BMS in the M18.
How are you tapping into the battery?
 
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