Reverse-Engineering Makita Batteries To Revive Them

Modern lithium-ion battery packs for cordless power tools contain an incredible amount of energy, which necessitates that they come with a range of safeties. Although it’s good when the battery management system (BMS) detects a fault and cuts power to prevent issues, there exist the possibility of false positives. Having an expensive battery pack brick itself for no good reason is rather annoying, as is being unable to reuse a BMS in for example a re-manufactured battery. This was the reasoning that led [Martin Jansson] down the path of reverse-engineering Makita batteries for starters.

After that initial reverse-engineering attempt involving a firmware dump of the NEC (Renesas) F0513 MCU, [Martin] didn’t get back to the project until recently, when he was contacted by [Romain] who donated a few BMS boards to the cause. One of these features an STM32 MCU, which made the task much easier. Ultimately [Martin] was able to determine the command set for the Maxim OneWire-based communication protocol, as was a hidden UART mode.

Due to the critical timing required, off-the-shelf programmers didn’t work, so an Arduino Uno-based programmer (ArduinoOBI) was created instead, which can be found on GitHub along with the Open Battery Information desktop application which provides access to these BMS features after connecting to the battery pack. Although only Makita is supported right now, [Martin] would like to see support for other brands being added as well.

34 thoughts on “Reverse-Engineering Makita Batteries To Revive Them

  1. OneWire is such a cool protocol. It’s a shame it never got an update, or much use, so many things that are currently done with just plain old “one wire per signal” could be OneWire if we had multimaster with interrupts and 5 cent GPIO controller chips.

  2. In my opinion battery packs are not expensive at all. You’re doing something wrong if your Makita saw, drill, impact or whatever didn’t pay for itself after a couple of jobs.

    This really is the golden age for people who are able to actually do something useful. Nouveau riche corporate drones fed a steady diet of UberEats, TikToks and Xanax pills are easily milked dry even on simple tasks, not to mention anything more “advanced” like basic carpentry.

    1. The power tool batteries may not be “expensive” in the sense you describe, where the cost of something doesn’t justify the benefit, but they sure are expensive in the sense of being marked up spectacularly compared to the actual cost of manufacture.

      Personally I have a massive collection of good 18650s harvested from tool batteries that suffered from the exact problem this project tries to address – they typically just had a single cell failure or were just slightly over-discharged, but since the BMS has decided to brick the unit for “safety” the packs got thrown out instead of repaired.

      Getting free salvaged cells has been a good deal for me, I guess, but I’d much rather I could just repair the damn batteries!

      1. While I agree its a shame they are not really repaired for what they are and can be used for I’d far rather a hair trigger BMS that prevents any potential dangers from sane use of the battery – The high powered tool is enough danger in its own right, really don’t want to have the battery pack burning in your hands while a potentially very heavy high inertia tool that will rip your hand bits or even kill you if you make a mistake is what you should be focused on…

        Not every power tool battery will ever get used in a tool of high enough power draw that a less than perfectly ideal battery is a problem, but some of these battery power tools are pulling really serious power and the design constraints inherent to be being a power tool battery make it much harder to deliver that much power safely than if you have more mass and volume to build your high power pack into.

        An official refurbished scheme (and so design for easy repair) where you can send in the worn out ones for discount or something would be great, and if they want to provide the information to repair your battery yourself I’d love that, shouldn’t even hurt the companies sales much if at all as most folks won’t actually repair the battery, or will buy a new one and repair the old – though from a liability and warranty on the connected tools etc standpoint it seems like it could be tricky to do.

        1. The other obvious point is that there needs to be a single specification for these battery packs. We’ve long since passed the point where these formats could even pretend to compete on features, and they’re all basically the same size.
          If these shared a common format, there’d be a healthy market in recycling them, because they do tend to fail with a lot of value left on the clock. It’s not viable now because you’d have to handle ten incompatible formats, and probably get sued regularly.
          This is a case where you can’t just tell manufacturers to recycle their batteries, because they’d rather lose money on mail-in schemes no one uses than give up their valuable lock-in scheme. Until governments command them to support a standard, this battery-to-landfill pipeline isn’t going to shut itself off.

          1. That would be nice. Though I don’t think it is strictly needed and would be very hard to actually create a good rule for that wouldn’t cause more trouble than it helps
            – at what point does a user replaceable battery fall into this category – could you end up biting BT headphones, laptops etc? How many voltages, peak power, energy stored standards do you need to cover all devices?
            – Do they have to be true identical form factor and mounting hardware or is it sufficient to use the same pinout and signalling from the BMS (if any) so a cheap adaptor is enough?
            – Does every device need to now have a user swappable battery? If not the power tools will probably end up taking the easy way out and just go for built in cells. Thus making you buy even more of the actual tool bodies so you can keep working and losing that flexibility to swap to the right tool for the job. Which is even worse that the current battery being ‘dead’ and not refurbished, but not so terrible everyone will go back to mains powered power tools as cordless is just handy.

            Plus with how long some big brands have kept the same battery standards recycling their batteries should be very viable – lots of them around and so many tools that would use them as they are compatible for a decade or three… So at least for those brands that have decided not waste R&D money to change battery shape, pinouts etc for no reason other than to force the customer to buy replacements for all their working bits when the last battery dies and they don’t sell replacements any more…

          2. @Foldi-One
            >Does every device need to now have a user swappable battery?
            Yes, please. Just sell me a case where i put in my normed 18650s or even make the devices accept these cells in the old school way with a normal battery compartment.
            And if the EU has to force the companies to do that, so be it.

      2. Also I’m not sure they are as marked up as you claim – assuming the brand name battery are using actually high quality cells even in bulk you are talking pretty huge cost per unit in the battery cells alone, add in the BMS circuitry, plastics, R&D costs and probably almost entirely if not entirely manual human assembly line…

        No doubt the official battery are not cheap, and no doubt they are making money (as they should be) but I don’t think its nearly as bad as you imply. At least not unless in your region the battery really are marked up heaps more than here for some reason. The cheap 3rd party and fakes can be so because they are really really crap in comparison. And are generally not actually that much cheaper for something that may be only barely useable with vastly less peak power and less energy stored than on the sticker (so compare that 3rd party 5Ah to the 2Ah from the brand in price for fairness (ymmv)), and certainly will be dead in very few charge cycles…

        1. I think my post must have come across as a more extreme position than I intended. I largely agree with you, though I still submit that power tool batteries have a substantially higher markup than many other batteries designed to do the same thing (as in, to the best that I can assess, ones that have essentially the same bill of materials and design goals, but the motor or load they’re powering isn’t a “power tool” per se.)

          Nearly all the brand-name power tool batteries I’ve taken apart have been built with quality cells and a sophisticated BMS that does everything it ought to, including the kind of overcurrent and temperature protection you absolutely want for safety in a high-current, harsh environment application. Even the “cheap” tool brands don’t seem to skimp on this. Cynically, I suspect this is because of liability concerns rather than any actual commitment to safety or pride in engineering, but the end result is what matters.

          And we’re definitely better off with batteries that refuse to work in a potentially unsafe situation than ones that catch on fire, explode, or do something else dangerous – I didn’t mean to imply that these features are bad in general, that they’re some kind of conspiracy by the manufacturers to sell more batteries, or that any person off the street should be able to flip a switch and re-enable a bad pack without knowing why it failed.

          But.. in the case of the Makita batteries in the article, I think things go beyond erring on the side of caution into absurdity (and there appear to be plenty of similar behaviors across other brands). Having the battery pack brick itself after it mysteriously fails a few charge cycles is one thing, but maybe at least *try* to identify the benign reasons?

          Or at least some hint for the end-user/hypothetical battery service center that this is why the battery suddenly stopped working?

          1. Yeah text and regional use of language differences can make it hard to be sure of the real intent behind the words, so please forgive me if you think I over reacted.

            Though having looked at the cost to rebuild a few power tool battery the price for actually high quality cells from a reputable distributor even if you assumed you were buying insanely vast numbers does add up quite quickly, and these tool battery will have 8? 10? 12? 16? even more? of these cells – at least in the case of the battery I looked at you couldn’t do a full rebuild with the same high quality fresh cells for much less if any less (I think it worked out more expensive right up until you were ordering 1000 battery at a time) than the cost the assembled powertool battery in the first place as an individual. Really its the abundance of identical looking and often hilariously over rated battery cells that are available basically for free that makes the power tool battery look bad.

            >Or at least some hint for the end-user/hypothetical battery service center that this is why the battery suddenly stopped working?

            That would be great, though the liability type stuff in the modern world could make that tricky.

            >I think things go beyond erring on the side of caution into absurdity

            Very tricky to really judge, as we don’t have the heaps of testing the legitimate brand presumably did before setting whatever BMS safety trips they did. And I think it part this comes down to these are powertool battery, which means they may be asked to go from full to empty really really fast and need to safely deliver that huge current yet have to built into durable boxes that are non-conductive to be safe on the job site.

            Other than other brands of power tool battery I’m not sure there is another good comparison for the electrical performance a power tool battery can require that isn’t in the RC world or the like where the battery generally is just a cell array with no protection at all, so will need a careful balanced charge after every use, and almost certainly will go puffy rather fast if the user isn’t very very careful… Maybe the personal electric vehicles but they tend to be both higher voltage and larger capacity. Sure most folks only use them on something comparatively lower power like a drill, but the angle grinders and up in power consumption needs still COULD be what they are used on next – so the powertool battery better render itself safe if it can’t hack those tools.

            Now a limp home mode vs full bricking I guess is a possibility with more complex BMS setups, though I think would for most users it would end up more annoying – Pull the charged battery out of the drill/worklight as you need to make one more cut, but its in limp home mode and can’t power that tool, cycle though all the ‘charged’ battery trying to get your cut done and now do you have any idea which battery are actually factory fresh and good for the more demanding tools?

      3. Battery packs are ridiculously expensive because they’re not standardized like say USB. Just force manufacturers to choose one standard kind of battery pack connector for each power class and have all products conform to that, and competition will bring prices back to normal in a breeze. Proprietary connectors and standards are the way companies fight against competition and should be eliminated or highly regulated.

        For those unaware, there are adapters to use battery pack X with tool brand Y, so that you can use your favorite battery packs with all your tools. They don’t contain any electronics so they’re really cheap.This is totally possible if they’re voltage+current compatible which is often the case; just search the usual sellers for [tool brand]+battery+adapter.

        1. I’m surprised the EU hasn’t mandated standardization on these battery packs to reduce e-waste, allow cost effective refurbishment and lower initial costs. Their is no advantage to proprietary packs except for the OEM to lock in customers.

    2. Whilst they’re not priced badly for professionals, they’re too expensive to be a consumable for hobbyists, who aren’t getting paid for using their tools. As the number of off-brand options shows.

      And even if you are getting paid, reducing costs is good. If you don’t agree, please send me your old battery packs after you’ve used them for one job!

      But regardless, the point of this is more to reduce waste, as the failure mode of battery packs is usually that just one cell has failed, and the rest of the pack is fine.

      1. The amount of batteries going in the trash is mind-blowing. Thankfully the replacement cordless razor I just bought was crap and I returned it, although Amazon will probably just throw that in the trash so no environmental savings there, but new rechargeable razors are cheaper than their replacement blades. I went back to my old one in spite of itself, but the one before this I even replaced the batteries myself. Cost effective? No. Environmentally useful, hell yeah.

    3. “pay for itself after a couple of jobs.”

      This is terrible it takes you a couple of jobs to pay for your tools, you should be able to do in under a single job, otherwise you are doing something wrong!

      With battery packs being so not expensive, most people don’t bother recharging them and just throw them away after a single use. Why waste time recharging them….

      1. “you should be able to do in under a single job”

        This is terrible if you have to actually start a job. You should cover 3x the cost of the tool before lifting a finger – get paid upfront !! Otherwise you’re doing EVERYTHING wrong. Why waste time plugging a battery into your cordless tool unless ….

        1. You guys are all nuts. I won’t even answer my phone until a client preemptively pays for all the tools needed for the job, plus the vehicle I drive to the store to pick them up. Suckers, all of you.

          1. FOOLS ALL

            You’re doing everything worse than wrong if you’re not born into a hereditary position as absolute monarch. Your subjects should be competing to please you by doing work for you before you even know you need it. The whole point of the value chain is to be at the top end of it.

        2. “You should cover 3x the cost of the tool before lifting a finger”

          This is terrible if you are having to get jobs, even if they pay up front and you do not have to do the work. You should be selling job futures, covering x10 the cost of the tools, otherwise you are doing it wrong.

          Why waste time with tools, just throw them away rather than plugging in the battery, even if they were never used it, makes more economic sense… just by a new one when needed.

          1. I break out a sweat just thinking about how inefficient you guys are. I think about customers, I think about buying tools, I thinks about invoicing, and then I think about cashing the check. I don’t even have to have a vehicle.

            …back to the subject at hand. Having rebuilt some failing packs, I was lucky to have the BMS accept the new cells. Being able to “restart” a BMS is a nice tool in itself.

    4. Contractor/handyman here. I had a young lady call me in a panic because the inspector was coming to do the inspection on her home and she didn’t have “the special tool” needed to remove the hatch cover to access her water heater.

      She paid $150 because I had a Philips screwdriver.

      1. That is awesome you were able to ripoff a young lady for so much money for so little work. But I guess that is pretty much the norm for contractors/handymen these days?

        1. I dunno, there’s a reason there’s a minimum cost of sending someone out on any kind of a call, and jumping the schedule for an emergency has a cost too. If you want it to be cheap/free, they need to establish over the phone that only a screwdriver is needed and the client will not need one delivered. Just like if an IT person had to be called out only to find that everything works as soon as they press a power button or plug something into the wall outlet, you’re paying for more than the actual five minutes on site.

          1. “Have you tried turning it off and on again?”

            You do have point there, but I feel usually good IT folks can get the simple stuff out of the way without racking up a hefty call out fee. Although that said there are a lot of shitty IT folks out there that like to guard/gate-keep petty knowledge due to ego and the perception of power.

            Of course now I am remembering the Psychic Friends Network vs Microsoft Technical Support article. If I remember correctly both were evenly matched with technical solutions, but PFN was cheaper and nicer to deal with.

          2. “Yes, of course, don’t treat me like an IDIOT!!1!”
            Spoiler: they did not, and now you blew it by asking that question. You’re going to have a call-out, a complaint, and absolutely no cooperation.

            Too often, IT is blamed when they can’t get people to meet them in the middle when it comes to the burden of communication. Sometimes it even devolves into stupid tricks, stuff like “Can you pull the cable out and tell me what the end looks like? Can you swap the ends?”.

            Of course, there’s terrible call-center support, but a lot of times the problem there isn’t petty IT people, it’s that you must first get past the wall of poorly communicating powerless script-followers. If you have a hard time with more capable support, often it’s really that you’re butting against management or their policies, although good IT will hopefully help you to know what the best they can do is without as much wasted time all around, and bad IT will exert their own petty power here.

        2. If someone can’t describe down the phone what’s wrong / needed or send a photo then 99% of the cost is the fixed costs of getting in the van, driving to the location, and filling in all the paperwork etc. afterwards, whether the job takes 1 minute or 1 hour the cost of getting there with the tools & experience is the same.

          Or put another way – if someone doesn’t have the wherewithal to google something so simple then they have to pay.

          What’s that old story about it being $1 for the chalk mark and $150 for knowing where to put the chalk mark?

        3. As someone who has chosen to learn how to do pretty much everything I’ve never needed to hire a contractor.
          Of course, if I couldnt be bothered I guess I would have been happy paying $150 for someone else to fix my laziness.

          I’m amazed at what people are unable and inept at not being able to do. Very simple things. Like wire a plug. And then are willing to pay someone else rather than learn.

          Think of it as a $150 education and they failed the exam.

  3. This is a common issue. What sucks is that there isn’t a “jumper” means to reset the BMS chip. I’ve experienced this with Lenovo Thinkpad batteries (sit too long), and in another case a 20V 2 AHr tool battery one brand of gas lawnmower uses for electric start. High starting current tripped out the BMS. The 18650 cells are just fine, and even when fully recharged on the bench power supply, the BMS won’t turn the FET’s back on. Soooo… solder across the FETs and it all works, but no more BMS… no more safety.

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