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Balance your Milwaukee M12 batteries!

Thanks to @istl I made new leads and have a battery balancing and making real progress, where this same M12 2.0 Ah battery was trying to balance through those 1kΩ resistors.

The downside is that it requires removing the outer shell of the battery.

If you just want to measure the cell voltages, all are exposed (and labeled) on the connections.
1698183414461.png

The case disassembles pretty easy and there are a few different styles, I'm sure Google can help it isn't obvious on your pack.
There are a few different circuit boards as you can see in post 21.
Anyways, here's my connections.

1698183664408.png

Well, in the 10 minutes I have been typing this and getting pics, the imbalance went from 120 mV down to 5 mV
Once I get this pack balanced, I'll capacity test another pack before and after balancing to see the improvement.

Lt.Dan said:
I'm the oddball with a lot of Ryobi tools. My oldest being my 1/2" Impact, it's been through about 5 or 6 years of daily mechanic work, doing tire rotations etc, and my oldest battery being a 4ah. Both the battery and impact are 12 years old now. The battery shows signs of aging, as the tools aren't as snappy compared with a newer battery, and it's average run time is shorter, but damnit a 12 year old battery is really impressive!

I would like to swap over to Milwaukee, but its hard to change over when I already have THIS many Ryobi tools/batteries.
Click to expand...
Yeah, I had a different brand tool before switching to Milwaukee, but Milwaukee has just so many tool options for specialty tools and the M12 line is inexpensive and quite capable. I've been happy since swapping to Milwaukee about 5 years ago.

When this impact released there was nothing like it, high torque for the compact size. This is why I made the swap, now there is plenty of competion, but I still like it.
www.milwaukeetool.com

M12 FUEL Stubby 3/8" Impact Wrench | Milwaukee Tool

MILWAUKEE® M12 FUEL™ 3/8" Stubby Impact Wrench is the industry's most compact cordless impact wrench at 5.1" in length, featuring 250 ft-lb of breakaway torque, and 4-mode drive control
www.milwaukeetool.com www.milwaukeetool.com
 
Heck, home depot has a deal right now, I just spent 199, and got a m12 impact driver, a 1/2" drill, soft case, a 2.5Ah and. 4Ah battery, and a charger...
 
Home Depot is the spot for Milwaukee deals.
The website has changed a bit they make it harder to find the SPECIAL BUY section.
Scroll to the bottom and click SPECIALS AND OFFERS.
Then scroll to FEATURED BRAND SAVINGS and click Milwaukee.
Then click 40% OFF OR MORE.
 
400bird said:
When this impact released there was nothing like it, high torque for the compact size. This is why I made the swap, now there is plenty of competion, but I still like it.
www.milwaukeetool.com

M12 FUEL Stubby 3/8" Impact Wrench | Milwaukee Tool

MILWAUKEE® M12 FUEL™ 3/8" Stubby Impact Wrench is the industry's most compact cordless impact wrench at 5.1" in length, featuring 250 ft-lb of breakaway torque, and 4-mode drive control
www.milwaukeetool.com www.milwaukeetool.com
Click to expand...
I like it too. I've got an m18 collecting dust because this m12 has the same torque AND it gets in tight spots.. I use it almost every day at work. Think I'll check cell voltages for fun. Thanks for the post.
 
I checked out my one bad M12 2.0 battery that wouldn't charge. I was only getting voltage from one cell using the small terminals on the outside but 12 volts from the main terminals. I opened up the case and tested each cell and they all have the same voltage. Ordered a new BMS board from amazon for $5. Hopefully it works out and I fix a $30 battery for $5!
James
 
Any recommendations for a balancer that will work well with M18 packs?
I have an 8ah that I suspect is way out of balance.
 
All 3 of my M18 packs were well balanced. Within a few millivolts. It was just the M12 batteries.

The M18 appears to have a real BMS, it doesn't expose cell voltages at the tool connection. You need to open up the pack to measure voltage right at the cells/bus bars.

An iCharger X8 would work well.
 
Thanks I'll check that out. I have some security torx bits on the way (of course I have every size but the one I need) so I can open them up and meter what's going on.
 
I took apart my 9.0 m18 battery and checked the cells. There are 5 sets in there and 1 set was at 3 volts, 1 at 3.8 and the other 3 sets were at 4 volts. I charged each set with jumper wires with magnets to hold them on from a single cell charger. Took a while! Now with all the cells balanced it should be good. Will test it today on a circular saw. I won't use the rapid charger any more, I've heard this is why it's unbalanced. It charges too fast and if any sets of cells are lagging behind it will stop charging when either set reaches a set voltage leaving the other sets not fully charged. I've got regular chargers on my service truck and some of my batteries I use at work are 5 years old and still working good. This 9.0 battery I use at home for my chain saws and weed eater. It would be nice to have a charger that would balance them without having to take them apart. I guess an adjustable bench charger set at the correct voltage for 5 cells in series?
James
 
JamesRich said:
I checked out my one bad M12 2.0 battery that wouldn't charge. I was only getting voltage from one cell using the small terminals on the outside but 12 volts from the main terminals. I opened up the case and tested each cell and they all have the same voltage. Ordered a new BMS board from amazon for $5. Hopefully it works out and I fix a $30 battery for $5!
James
Click to expand...
The $5 bms from amazon fixed my battery! Now it charges normally and I can put it back in rotation.
James
 

This is the bms i got that fixed my M12 battery. The bms should show each cells voltage through the terminal tabs on top like 400bird's photo above. Mine only showed voltage across the two main terminals. I had used this battery infrequently at home on a hackzall to cut branches before it went bad. It's in my service truck now on rotation and is still holding up.
I used the M18 battery i was having problems with yesterday to build a project and its working great again. I kept swapping it from tool to tool to run it down. Had to finish it off on a vacuum just leaving it run. This forum has taught me a lot about batteries and saved me quite a bit of money just on these two batteries!
James
 
Nice fix! Do you know if your replacement M12 BMS has high value resistors between the cell taps and cells?
 
Most of the batteries i have that wont take a charge have a dead cell...
My m12 6ah has a pair at 0v a pair at 4.1v, and a pair at 3.2v...

I figure i have to replace the cells...
No fun on the xc packs.
 
Used M18 for almost 20 years I guess the first combi drill I bought was brushed think I replaced the brushes a good few times and the gearbox eventually packed in about 10 years ago next drill packed in a week out of warranty newer stuff wasn't built like that but it's still not bad.
Moved to M12 five or so years ago ( just so I could stuff a drill in my backpack) and learnt early the batteries are trashy. I haven't pulled a tool apart yet but when I do I will hunt for that BMS because I'm guessing it has to be there.

I've trashed way to many batteries on my DIY boombox for there to be anything resembling a BMS inside. Have a stack of batteries disassembled on my bench I haven't bothered to order cells for yet. Had issues with a few of the parallel style batteries but after a few jump starts and a few days after charging letting the cells balance each pair they worked and charged fully.
 
SparkyJJO said:
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.
Click to expand...


I have older Makita stuff and it works great but the batteries were tired old NiCads and not working so well - I had a couple of the newer items for a week to build fence and returned them in favor of Milwaukee... The difference is power, torque and battery life is pretty stark.
 
Lt.Dan said:
I'm the oddball with a lot of Ryobi tools. My oldest being my 1/2" Impact, it's been through about 5 or 6 years of daily mechanic work, doing tire rotations etc, and my oldest battery being a 4ah. Both the battery and impact are 12 years old now. The battery shows signs of aging, as the tools aren't as snappy compared with a newer battery, and it's average run time is shorter, but damnit a 12 year old battery is really impressive!

I would like to swap over to Milwaukee, but its hard to change over when I already have THIS many Ryobi tools/batteries.
Click to expand...
Nothing oddball with being a ryobi guy. Those tools are well built when considering the price. If they all get stolen you dont need a bank loan to replace. The aftermarket batteries are cheap. When Home Depot has the tools on sale is worth the wait. They are not as strong comparing to Milwaukee. If I burn a ryobi down trying to finish a job it was well worth the expense. May it now rest in piece(s).
 
The real problem with tools these days is that there are only about 4 actual manufacturers and the rest just have them built to spec.

Black and decker - craftsman - dewault - all the same vendor, different labels
Milwaukee is the same mfg as Ryobi
Rigid/harbor frieght/no-name tools/tent vendors

There is a large list someplace for the different brands verse vendor names - in some cases they are on the same factory floor or assembly line but to different specs with different quality bearings and the like.

IMO the dewalt stuff took a quality dive when Black & Decker bought them.
 
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