[HN Gopher] Milwaukee M18 Battery Reverse Engineering
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Milwaukee M18 Battery Reverse Engineering
Author : jakogut
Score : 103 points
Date : 2025-04-17 16:07 UTC (6 hours ago)
(HTM) web link (quagmirerepair.com)
(TXT) w3m dump (quagmirerepair.com)
| Liftyee wrote:
| Always love to see an in-depth reverse engineering write-up. This
| one's particularly interesting since I'm currently designing a
| battery pack for my own project.
|
| Interesting to see a microcontroller (and quite a classic one...)
| as well as an ASIC for battery management. I imagine it's for
| communication purposes. The battery management chips I've been
| looking at have built in I2C interfaces to let me avoid firmware.
| alnwlsn wrote:
| I've been down this road before. The ASIC in the Milwaukee pack
| is known as an "analog front end". Since you can't wire cells
| directly up to the pins of your MCU, you have a chip to handle
| that stuff for you. It will let you read the voltage of each
| cell in the stack (some are literally analog, and just provide
| a nicely in-range voltage output for your MCU's ADC to read;
| others have internal ADCs). It might do current sensing. It
| might handle a couple alarms to turn off a mosfet when things
| go wrong. It will have an I2C interface, but the supported
| commands are "tell me voltage of cell #2" or "put shunt
| resistor on cell #1 for balancing". It's still the MCU that
| calls most of the shots here, but the more advanced ASICs can
| do more things autonomously.
| whalesalad wrote:
| As a heavy user of Milwaukee gear this is a very pertinent and
| interesting analysis.
| gcormier wrote:
| https://www.youtube.com/watch?v=q7spzrIbdKY
|
| This guy has a few videos on his channel dedicated to the
| batteries.
| glitchc wrote:
| I'm not sure I follow. Aren't all lithium charging circuits
| basically the same nowadays, namely an SMC paired with a voltage
| pump or switching power circuit?
| s_tec wrote:
| This isn't the charging circuit - that goes in the charger.
| This circuit is responsible monitoring the state-of-charge (for
| that little LED bar graph on the front), disconnecting the
| cells if something goes wrong, and negotiating available
| current with the tool. It _should_ also be responsible for cell
| balancing, but it looks like Milwaukee forgot to implement that
| feature (oops).
|
| The videos at the bottom of the article have most of the
| details, since those dive into the communications protocols as
| opposed to the raw schematics.
| Saris wrote:
| Their M12 batteries don't have balancing (or a BMS inside),
| so they go out of balance and 'bad' very quickly. I've just
| added a balance plug to the outside of mine that I plug into
| my hobby Li-ion charger.
| nicolaslem wrote:
| Fun fact, DeWalt 18/20V batteries also don't have
| balancing. The batteries have pins going to each cell for
| it but no chargers actually use them.
| Saris wrote:
| It's such a strange thing to do unless they wanted to
| intentionally make them have short lifespans.
|
| The M12s have the pins too for voltage sensing in the
| charger (and tool maybe?), but they have 1 mega ohm
| resistors in line so cannot be used for balancing.
| zippergz wrote:
| I believe you on the technical details, but as an anecdote,
| I have M12 batteries that are 10 years old and still
| working fine. At least, good enough that I have noticed no
| issues with them and I don't even know off the top of my
| head which of my batteries are newer and which are older. I
| also have a bunch of M18 tools and batteries, and I've
| noticed no particular difference in how they age compared
| to the M12 ones. But I'm just a DIY homeowner, so my usage
| is relatively light.
| Saris wrote:
| Yeah I figure most of them work fine, otherwise I'd find
| more similar stories.
|
| We have about 10 of the M12 batteries, about half are the
| 3 cell ones and half the 6 cell larger capacity ones. And
| every single one has gone completely out of balance
| within 2 years of use.
|
| I plug them into a balancer and they last another solid 6
| months or so.
| glitchc wrote:
| There are always two charging circuits for Li batteries, one
| in the battery and the other in the charger. They pair
| together to negotiate the voltage and current. There's a
| dedicated protocol to do this.
| teraflop wrote:
| This is absolutely not "always" true. There are tons of
| 18650 cells that have no electronics whatsoever, and there
| are tons of dedicated charging ICs that connect directly to
| cells/batteries.
| throwaway48476 wrote:
| The EU is forcing toolmakers to use standard batteries. Hopefully
| we can get them in the US too.
| aequitas wrote:
| Do you have a source for this? Because all I know is that this
| was an April fools joke from last year. I'm curious of the EU
| is now actually doing this.
| toomuchtodo wrote:
| Edit: Bamboozled by the search gods
| kube-system wrote:
| That appears to be the abovementioned April Fools video.
| AlexandrB wrote:
| This would be painful in the short term because all my current
| tools and batteries would likely become obsolete, but it would
| be cool to see manufacturers more vigorously competing on
| battery specs like power and energy density.
|
| There's also the risk that tool prices could go up as I suspect
| some tools are currently sold as a loss-leader to get you into
| "the system".
| MisterTea wrote:
| > This would be painful in the short term because all my
| current tools and batteries would likely become obsolete
|
| I have seen 3rd party battery accessories so anyone looking
| to make money might wind up making adapters to retrofit
| tools. Good for the environment too.
| fragmede wrote:
| https://powertoolsadapters.com/ specializes in exactly
| this.
| bombela wrote:
| For some reason they insist in shoving some USB PSU in
| many of those adapters.
|
| That will drain the battery by itself over time. So you
| then must make sure to remove the battery from the
| adapter as per instructions.
|
| That is just so dumb, it's beyond my understanding.
| whalesalad wrote:
| We've had universal adapters for ages. You can run a DeWalt
| battery on a Milwaukee, Makita on DeWalt, etc. I even have an
| adapter to run my Milwaukee M18 batteries on my Dyson vacuum.
| You can run a wire to the pos/neg leads on the battery and use
| it standalone. I use it to power temporary reverse off-road
| lights on my truck. I see no reason to do this sort of thing.
| More oppressive regulation from the EU that no one actually
| wants. Fortunately Milwaukee is a US company as well as a
| dominant player in the market and will likely not participate
| in this whatsoever.
| buescher wrote:
| Milwaukee was a US company but has been a brand of Techtronic
| Industries, which is based in Hong Kong, for about 20 years
| now.
| johnwalkr wrote:
| Too bad this wasn't real, especially since at the end of the
| day, all these things are just using 18560 cells.
|
| I tried to standardize on one system (Hikoki 18/36V). This was
| great as they use the same battery across consumer and pro
| products. But I moved from Japan to Europe and they are far
| less available, and more expensive. Now I buy Parkside stuff
| (Lidl brand) and they are probably a tier lower but better
| value and also use the same battery across consumer and pro
| products.
|
| Anyway I felt lucky that I could buy both low and high(er) end
| cordless tools in two countries/brands and also find adapters
| to use both batteries in both sets of tools. Both systems don't
| have any sort of data handshake between tool and battery. Going
| forward, this will probably increasingly be the case so I would
| love for a standard to be enforced.
| tomcam wrote:
| FWIW I find these batteries and the charger to be exceptional.
| You can just leave batteries in and it knows when to stop
| charging. If you get the big charger and put a bunch of batteries
| in it charges them round-robin style. And the batteries
| themselves seem to be sturdy, robust, and high capacity. They're
| also expensive af so you want to wait for a sale if possible. I
| even spent a ridiculous amount of money on the battery-powered
| wet/dry vac and haven't regretted it for a moment.
| bombcar wrote:
| I never buy the batteries - I always look for a tool with the
| battery, as you can almost always score a free tool (or free
| battery depending on how you look at it).
| cameron_b wrote:
| I have three M18 batteries that are from 2011, and have
| outlasted 4 Ryobi batteries that get much less abuse.
| linsomniac wrote:
| I just switched over the last 6 months over to Milwaukee tools
| for my home DIY stuff and they are really exceptional. I got
| one of the 7 1/4" circular saws with a FORGE battery and it
| just cuts everything I've thrown at it effortlessly. I'd put it
| as more powerful than my Dewalt 10" corded tablesaw, at least
| it seems much happier to rip a 2x4 than the table saw. I even
| designed a 3D printed sled for it to run on my track saw tracks
| and it does a great job there.
| bityard wrote:
| One Christmas, I was given a shiny new 14.4V Craftsman NiCad
| drill with two batteries. These were not cheap and I was young
| and broke and very grateful for the thoughtful gift. It worked
| great and I enjoyed it immensely. For about a year.
|
| After that, neither pack would hold a charge long enough to be
| useful. Which I thought was pretty disgusting. Come to find out,
| this was basically the normal standard to which Craftsman had
| finally sunk. Rather than do the rational thing and throw it out,
| I held onto it with with a grudge and a goal of actually making
| it useful again one day.
|
| A few years back, I found a decent deal on brand-new 18650 high-
| current LiFePo4 batteries from a reputable supplier ($2.50 each,
| sadly NLA) and bought up a bunch to remake the packs for this
| drill and a couple others I had laying around for similar
| reasons. I added an inexpensive but well-made BMS (which I tested
| thoroughly before implementing) and the voltage was upped to 16V
| nominal for a little extra kick. Don't ask how I spot-welded the
| tabs to the batteries.
|
| 4.5 years later and these drills are still going strong, I use
| them at least once a week on both small and large projects. They
| are not speed demons or torque monsters, but they drill all the
| holes I ask them to. Would I have been better off economically
| throwing these ones in the garbage and just buying the cheapest
| thing from Harbor Freight? Maybe.
|
| But spite, it turns out, is its own reward and I would do it all
| over again a heartbeat.
| mitthrowaway2 wrote:
| It might not have been Craftsman's fault; NiCad batteries are
| vulnerable to the memory effect, which means if they were not
| fully discharged when you recharge them, the maximum capacity
| shrinks.
| xenadu02 wrote:
| The Ryobi lithium batteries I got with my first cordless drill
| bundle at Home Depot in 2006 still work and still hold a useful
| amount of charge today. And the charger I got back then will
| charge the newest batteries - not as fast - but they charge.
|
| Pretty amazing compared to what all batteries were like growing
| up in the 90s.
| devwastaken wrote:
| why cant i use an external DC power supply to replace the one in
| the chargers? no reason they cant be USB-c given proper supply
| but there seems to be some kind of special signaling.
| stuckkeys wrote:
| I appreciate the mild humor injected into various scenes.
| noefingway wrote:
| I have a substantial investment in both Dewalt and Milwaukee
| tools that I use regularly in my farming operation. I definitely
| prefer the Milwaukee tools to the Dewalt. I recently bought a 6"
| Milwaukee chain saw for light duty cutting. I get a lot of cuts
| before I have to change batteries. Also the torque in the
| Milwaukee 3/4" impact gun is truly amazing and the battery lasts
| through a lot of bolt removals.
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