Resurrecting imbalanced Milwaukee M12 battery

[OM617YOTA]

Pushed one of my M12 batteries a bit too far with my tire inflator and got the dreaded red/green blinking light of death when I stuck it on the charger. No chargy-chargy.

These batteries are made up of three sets of li-on cells in series to get to 12v nominal. There are sensing leads and contacts so the charger can measure the voltage of each cell, and if they get too imbalanced, shuts down charging and you get the red/green blinking light of death. There should have been a cell balancing system, but this is just a monitoring and "error - go buy a new battery" system. Note below, voltages are all different - the 4.002v cell was after charging. Resistors in the first pic were just convenient conductive objects of the right size to stick in the battery slots and get measurements.



Would be convenient if you could charge through these monitoring contacts, right? Too convenient - there's a high ohm resistor inline, likely to prevent short circuit. Could still be done, but would take weeks.

Disassemble the pack, hook the benchtop power supply directly to the cells, and let the electrons start flowing. To keep charging amps low, I kept charge voltage only slightly above cell voltage, bumping it up here and there as the cells charged. Have to be careful at this stage, with these connections I've bypassed the battery monitoring system and all the circuit protection.



Charged all the cells to 4v, then reassembled and slapped it on the Milwaukee charger. Success, no red/green blinking light of death, and it took a full charge.



M18 batteries don't seem to suffer from this problem, I think they have an actual cell balancing system, not just monitoring.

Lessons learned: Already knew this, but it really underlined that M12 isn't meant for high drain devices. When using high drain devices, make sure you start with full batteries, and don't push them until the tool shuts itself down. Soon as you hear the tool starting to struggle or slow down, stop and swap to a fresh battery. High drain devices really should be M18 wherever possible, and M12 should only be used in low draw devices where compact size and light weight are paramount. I have a ratchet and under hood light, perfect uses for M12. My shop vac and tire inflator, not so perfect.

 

[sean donato]

Unless something has changed, none of the 20 volt batteries have cell balancing, they do have a battery management system that shuts off power if voltage drops too low.

 

[OM617YOTA]

Just had this happen, again, on both of my "big" 6ah M12 batteries. Not sure if there's a problem with these batteries, but I can't recommend M12 tools for any kind of even halfway heavy work.

Going to do some research but it looks like I'll be selling my tire inflator and vacuum and buying M18 equivalents.

 

[OM617YOTA]

Doing some more research, it seems like this is a known issue with these particular 6ah M12 batteries, and the M12 system isn't as delicate as I thought. Guess I'll be sourcing some other batteries.

In the mean time I'll recharge these with the benchtop power supply until they die for good. Kind of a pain but not terrible.

 

[J D]

If you're handy with a multi-meter I'd be inclined to open the battery up & measure the individual cells before charging it like that. If they all measure comparably & one has just dropped under the threshold (& hasn't been that way for any length of time) then carry on. If there is any significant imbalance then further investigation is required if you wish to avoid further damage & the potential fireworks that can go along with.
I wouldn't needlessly overdrain them any further, but ideally measure the cells after the battery has had a bit of a load on it.

 

[OM617YOTA]

If you're handy with a multi-meter I'd be inclined to open the battery up & measure the individual cells before charging it like that. If they all measure comparably & one has just dropped under the threshold (& hasn't been that way for any length of time) then carry on. If there is any significant imbalance then further investigation is required if you wish to avoid further damage & the potential fireworks that can go along with.
I wouldn't needlessly overdrain them any further, but ideally measure the cells after the battery has had a bit of a load on it.

Read the rest of the thread.

 

[Stubby]

Boy...I wish that I understood this topic better...as far as "rebooting" a battery.

I have an Echo string trimmer and an Echo 16" chainsaw that take a 58 volt battery. I was very impressed with the performance of the chainsaw when I first got it. The string trimmer, too, but that doesn't require the same power draw from the battery that the chainsaw does.

Over time (a short time..maybe 10 hours of use), when I put a fully charged battery into the chainsaw, it would start out cutting ok, but after a minute or less, it would just quit. I wasn't forcing it, the chain was sharp. Plenty of battery power left....

I tried the battery "restart" procedure...press the indicator button on the battery for 5-10 seconds. The saw would run again, but only for a few seconds.

That same battery would operate the string trimmer just fine for the entire job of trimming our property (takes about an hour).

Now, I seem to have a situation...I have this chainsaw that I can't really use unless I buy another battery for 200 bucks. But, I'd hate to spend that much money on another battery just to get the same results.

But, I did. So far, the second battery works fine. I use the first battery for string trimming, and the second one for the chainsaw. I'd really like to buy a 3rd battery, to have 2 good batteries for the saw, but I probably wont. I have a handful of other saws that I can use, some gas, some electric.

Maybe I'll watch some videos on this topic and attempt to repair the first battery. I have one of those 12v power sources that I use for electrolysis rust removal.

Rich

 

[OM617YOTA]

Boy...I wish that I understood this topic better...as far as "rebooting" a battery.

I have an Echo string trimmer and an Echo 16" chainsaw that take a 58 volt battery. I was very impressed with the performance of the chainsaw when I first got it. The string trimmer, too, but that doesn't require the same power draw from the battery that the chainsaw does.

Over time (a short time..maybe 10 hours of use), when I put a fully charged battery into the chainsaw, it would start out cutting ok, but after a minute or less, it would just quit. I wasn't forcing it, the chain was sharp. Plenty of battery power left....

I tried the battery "restart" procedure...press the indicator button on the battery for 5-10 seconds. The saw would run again, but only for a few seconds.

That same battery would operate the string trimmer just fine for the entire job of trimming our property (takes about an hour).

Now, I seem to have a situation...I have this chainsaw that I can't really use unless I buy another battery for 200 bucks. But, I'd hate to spend that much money on another battery just to get the same results.

But, I did. So far, the second battery works fine. I use the first battery for string trimming, and the second one for the chainsaw. I'd really like to buy a 3rd battery, to have 2 good batteries for the saw, but I probably wont. I have a handful of other saws that I can use, some gas, some electric.

Maybe I'll watch some videos on this topic and attempt to repair the first battery. I have one of those 12v power sources that I use for electrolysis rust removal.

Rich

That's a battery failure. If you're still under warranty, it should be replaced.

 

[J D]

Read the rest of the thread.

I did... but I probably could have written my reply better.
You said when you checked the cells individually they were imbalanced, so you charged them individually, which is fine. Then you say the batteries have done the same thing again & show you are charging them of a benchtop power supply in the assembled (2p 3s) configuration. In that situation, if the cells are imbalanced again, you will be overcharging some & under charging others. Each time you repeat the process the imbalance will be worse & in short order a cell will fail completely (& possibly catastrophically).
It's likely one of the cells is failing & it's parallel cell will be carrying the load, charging/discharging at a higher rate & generally being overloaded.
If you charge the cells individually again, then load the battery & monitor discharge on the individual cells under load the problem cell(s) should stand out

 

[OM617YOTA]

I did... but I probably could have written my reply better.
You said when you checked the cells individually they were imbalanced, so you charged them individually, which is fine. Then you say the batteries have done the same thing again & show you are charging them of a benchtop power supply in the assembled (2p 3s) configuration. In that situation, if the cells are imbalanced again, you will be overcharging some & under charging others. Each time you repeat the process the imbalance will be worse & in short order a cell will fail completely (& possibly catastrophically).
It's likely one of the cells is failing & it's parallel cell will be carrying the load, charging/discharging at a higher rate & generally being overloaded.
If you charge the cells individually again, then load the battery & monitor discharge on the individual cells under load the problem cell(s) should stand out

These batteries are forfeit. Garbage. Junk. I'm not worried about a catastrophic failure, and I'm aware they'll get further and further out of balance. When they die for good or when I get around to replacing them, they'll go to recycling. That's all the effort I'm willing to devote to them.

 

[Chevboy0167]

This guy is pretty good with lithium tech. He may be able to answer some questions if you have them.

https://www.youtube.com/@HBPowerwall/videos

 

[Gardiner Schneider]

These batteries are forfeit. Garbage. Junk. I'm not worried about a catastrophic failure, and I'm aware they'll get further and further out of balance. When they die for good or when I get around to replacing them, they'll go to recycling. That's all the effort I'm willing to devote to them.

Our company makes hi temp, hi dialectric mica insulation for LI batts. If I were you, I would be worried about "catastrophic failure". If it happens when you are running your saw or weed whip, you can probably drop the tool, back off, and watch the fireworks from a safe distance. If the failure occurs when the battery is in the charger, in your shop, the fire could burn you out.

 

[thompsoncustom]

milwaukee low voltage protection is either in the tool or the battery recognizes the milwaukee tool only as if you use them to power other things you don't get the shutoff low voltage protection.

when I got the red/green light of death my quick and dirty way to get the charger to take it again was I hooks the milwaukee battery up to a car battery don't remember for how long but probably till it had 12v's at that point I was able to put it on the milwaukee charger and it took care of the rest. that was a couple years ago still works fine to this day.

 

[Stubby]

That's a battery failure. If you're still under warranty, it should be replaced.

I dropped the ball on that opportunity, unfortunately. Apparently these Echo batteries have a history of failing.

There are a lot of videos on repairing them, so I'll view a couple of them and see if I might be able to resurrect it...

https://video.search.yahoo.com/yhs/...&type=teff_10019_FFW_ZZ#id=&vid=&action=close

Rich

 

[OM617YOTA]

Alrighty, yet more research. Had to nail this one down, if it was a problem with these batteries then I'd be sourcing different batteries, if it was a problem with the M12 system in general then then the entire system was going to disappear from my life.

Luckily it's just these 6ah batteries. They are a failed product, this is a widespread and well known problem. These batteries have 1.9 stars on Milwaukee's own site and 2 stars on Ace Hardware, and the problem has it's own Reddit page.

Somehow I got lucky that mine have worked as well as they have for as long as they have, probably due to only owning and using them in low power devices. Once I got higher power tools, failure was inevitable.

Side note, Home Depot's site has page after page after page of 1 star reviews for exactly this issue on these batteries, and yet overall still 4.5 stars. Seems implausible to me, and I'll definitely take this into account when using Home Depot's star ratings to make purchasing decisions from now on.

This is the best deal I've found on replacements, 3 pack of 5ah batteries for $200, direct from Milwaukee's retail site.

https://www.redtoolstore.com/produc...attery-2-pack-w-free-extra-48-11-2450-battery

I'm happy to nerd out on plenty of things and explore the more esoteric corners of a subject I'm interested in, but M12 batteries just ain't one of those subjects. I've spent WAY too much time dealing with this.

 

[OM617YOTA]

 

[OM617YOTA]

Bad 6ah batteries, my inflator struggled to top up two dually tires without flatlining. Absolute trash.

One of the good 5ah batteries, topped up all six dually tires, plus all four Land Cruiser tires, and still had half the battery left, despite being in theory 1ah smaller. The M12 system is much more skookum than I thought, capable of doing actual work.

I'm impressed.

 

[J D]

Yup, when a lithium battery won't charge there is almost always a good reason.
That said, the reason may be relatively straight forward to correct safely (ie replace faulty cells) but a lot of manufacturers appear to be going out of their way to prevent this. The result is significant expense passed on to the user & considerable unnecessary waste. It also leads to hack repairs ("jump starting" of batteries etc) which under certain circumstances may be appropriate but can also be seriously unsafe

 

[trains]

Our company makes hi temp, hi dialectric mica insulation for LI batts. If I were you, I would be worried about "catastrophic failure". If it happens when you are running your saw or weed whip, you can probably drop the tool, back off, and watch the fireworks from a safe distance. If the failure occurs when the battery is in the charger, in your shop, the fire could burn you out.

A neighbor lost their entire house to a fire caused by charging batteries left overnight in the garage.

 

[Gardiner Schneider]

Trains,
I hope your neighbor and Family were uninjured in the fire, at least physically uninjured. I have never lost my house or boat to fire in my eighty years; however, my Step Father lost his, and carried the mental injury for the rest of his days. How many times did he awaken in the middle of the night and ask himself, why did I not unplug the Christmas tree lights that evening? Perhaps we should think of our LI batteries in their chargers the same way.