Balance your Milwaukee M12 batteries!

[400bird]

Any balancing success?

Wondering because there's a 1k resistor between the cell level wire leads and the per cell top terminals.

Damnit, there's definitely resistors on the C1 and C2 connections. This would take a literal eternity.
Also, there's no BMS in the M12 battery, I think/hope they include that on the tool side.

I'm going to have to rethink the easiest way to balance these, but it's going to require opening each pack.

 

[Tomthumb62]

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.

I got a good deal on a basic Makita drill and driver set with two 5.0Ah batteries. It’s about 5 years old now and have been used quite a bit, mostly building out our homemade camp trailer and things like chicken coops. I think they drain a bit quicker than when new, especially the one battery that has gotten used the most on the driver, but I’m very pleased with them. I did break the chuck on the drill but I was really abusing it by using some very large bits in it and was drilling through both 1/8” hardened steel and 2” thick planks of fir. Haven’t yet replaced it but our drilling days are done for the season, lol. If we need to drill a 1/8” hole, we’re good, because that’s the bit that’s currently stuck in the chuck.

 

[istl]

I was wondering why it's going slow as mud. I'm something like 20 hours into one battery.

 

[Supervstech]

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

I’m sure I have several M28 tools in the shop somewhere… they didn’t last long for me.

 

[Lt.Dan]

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.

 

[400bird]

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.


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.



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.

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.

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.

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

The 3/8" compact impact wrench is 5.1" in length, features 250 ft-lb of breakaway torque, and 4-mode drive control.

www.milwaukeetool.com

 

[Supervstech]

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...

 

[wopachop]

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.

 

[NorthTown2022]

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.

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

The 3/8" compact impact wrench is 5.1" in length, features 250 ft-lb of breakaway torque, and 4-mode drive control.

www.milwaukeetool.com

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.

 

[JamesRich]

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

 

[Millennium]

Brilliant thread, I'm amazed y'all figured this out.

I just returned my M12 Redlithium XC6.0 batteries to Milwaukee for replacements, under the 3-year warranty.

Milwaukee Service Dashboard

service.milwaukeetool.com

 

[istl]

Well, in the 10 minutes I have been typing this and getting pics, the imbalance went from 120 mV down to 5 mV

 

[42OhmsPA]

Any recommendations for a balancer that will work well with M18 packs?
I have an 8ah that I suspect is way out of balance.

 

[400bird]

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.

 

[42OhmsPA]

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.

 

[400bird]

Yeah, I never expected to use my ifixit kit on a Milwaukee battery, but that's the only reason I had the oddball size.

 

[Nobodybusiness]

Well, I've got a iCharger X8,

I love mine. Used to use it a lot back when me and the kids did a lot of RC truck stuff.

Never thought about using it for that but add a JST connector and some balance leads and it would work.

 

[JamesRich]

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]

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

The $5 bms from amazon fixed my battery! Now it charges normally and I can put it back in rotation.
James

 

[42OhmsPA]

The $5 bms from amazon fixed my battery! Now it charges normally and I can put it back in rotation.
James

Could you share which one you purchased?
Great tip on the magnets, thanks.

Edit to add I think the rapid charger is what messed mine up too.