Makita Battery Pack Repair

[Rob] grew tired of his Makita power tool battery packs dying so he figured out how to repair them himself. The video after the break walks us through the process which starts by cracking open the case. Inside there is a controller board and a battery of ten cells. [Rob] has pinpointed these battery failures to just the first cell, which is confirmed by measuring the cell voltages with a multimeter. The first cell in the demonstration battery reads zero volts and needs to be replaced. For some reason he’s got heck of a lot of these cells on hand, at the end of the video he shows off a massive block of them that provides one half of a kilowatt-hour of power.

To complete the resurrection he removed the control circuitry from the integrated PCB. It seems that the microcontroller on the battery’s PCB monitors it and bricks them when it thinks the life of the unit has ended. By hacking a charger he can now balance-charge the altered battery packs and get more use out of them before they hit the landfill.


69 thoughts on “Makita Battery Pack Repair

  1. It’s a bad idea to replace a single cell in a pack like this. If the cells don’t discharge evenly you can get in a situation where a strong cell reverses a weak cell. That will drastically shorten the life of the reversed cell or even destroy it (depending on which battery chemistry it is).

    This is the same reason why instruction manuals for everything state to use only matched, new batteries when you replace them. You can get away with a lot in something like a remote control, but in a high-current application you have an opportunity to rupture a cell.

  2. These 18650 Li-ion cells are great. I recovered about 200 of them from dead laptop batteries in the recycle bin at my former job, fixed up all of them except for about 1% (totally unrecoverable), contrived a charge controller, and configured a rechargeable battery bank to run my porch lights in the summer time.

    The biggest pain is connecting all cells together.

  3. While I appreciate the time he took to show his process,and his big ass LiOn pack is cool…he didn’t really show anything that someone who decided to open the pack couldn’t find on his own.Matched cells are a figment of the imagination of battery pack manufacturers.The intention is to make you buy a new pack.I have made hundreds of battery packs out of used cells.Never had an explosion or a fire.Now do these packs last as long as fresh commercial packs? probably not but who cares I have 30 of them and they were free.

  4. hmm.. i have used bare li-ion cells before to repair dvd player battery packs.

    usually it works, but be very careful as they can easily runaway and ignite if mistreated.

    a123 cells are better, dewalt packs use these and they are a lot nicer. no runaway problems and usually they charge up fine.

  5. Ben, your cautionary advise is right out the safety sheet for sure. My point here is if you care to grow a pair, you can get more real world useage out of your battery packs by replacing the one cell that goes bad until it becomes a PITA to keep doing that repeatedly.

    I disagree, it’s highly unlikely that any such battery pack will be subjected to such high current discharge as to become dangerous – far too much engineering has taken place to prevent that from happening in the first place. Homemade bundles with high current straps is another subject entirely and there your cautions become good advice.

    1. Thanks for putting things into my perspective. I was thinking I could easily pick up a few Makita batteries from the recycle bin and use some of the decent cells to resolve some issues that are bound to happen over time with my Makita, saving money and the planet while doing it. DAF

      1. My son-in-law said the process I used on his Milwaukee 18v battery pack worked on his pack. What I did was to open it, and charge the batteries on the + and – ends of the batteries directly. Did this with a DeWalt one hour charger. then told him to put in his charger when he got it home. Do Not use before running it through a charge cycle first. I though this might reset the on board circuit board. Guess it did, said it worked like new now. Oh, I didn’t do the batteries one at a time. Look for the pos. & neg. points on the string of batteries.. First & Last ends.. Alligator clips on these points and ran a one hour charge cycle, red light when charging, steady red light when charged. Volt meter showed 19,2 volts after charge stopped a short time later. maybe it will work for you..
        use at your on risk though…..they can explode also!!!!!!!!!!!!!! July 1, 2014

  6. I tend to put a few thermesistors in between the gaps in my big battery packs with a simple controler circute to shut off charging/high current draw if they get too hot
    also tend to put a few pc fans blowing air through the battery pack to cool it (saw it in a battery pack from an expencive drill on a small scale and so scaled it up for my application)

    best thing to do with lithium batterys has to be to split them open um role the lithium metle and drop i a SMALL bit at a time into a STRONG container with a bit of water (dont add too much id you must give it a go it explodes also only do tuos oit sode never in doors or in a shed į know it seems obvious but there are some really silly people out there lol

  7. @Carl
    Seconded. Inconsistent units really irk me in technical writing. If “power” was intended, the units should read “half of a kilowatt.” If you don’t know what was intended (among current, potential, power, energy, etc.), either research the source more, or if you’re naively quoting the term “kilowatt-hour” you might get away with something like “half of a kilowatt-hour of juice”, where “juice” is ambiguous and lets the reader deduce the primary source’s intended form.

  8. @Lee
    “far too much engineering has taken place to prevent that from happening in the first place”

    Don’t put too much faith into the built in safeties of Lithium batteries. They may protect you from catastrophic failure some of the time, but even the safeties can fail. We have had a lithium battery explode in out test room, not catch fire, explode. If our lab tech was in the room he would have been severely injured. Sure you can hack cells together into refurbished packs, and they will kinda work, but it’s not worth the risk.

    On another note, when building a Li-ion pack for a project, be very wary of cheap chargers. I’ve seen a battery pack/charger combos that use a Ni-Cd charge routine to charge Li-ion batteries. Ni-Cd chargers can’t detect the end of charge of Li-ion and basically keeps charging until the protection circuit opens.

  9. Are there any lithium battery testers out there that can charge up a single or multiple cell pack then discharge it to the safe level to find out the capacity of the cell/pack?

    I have a pretty good charger that can do that for AA/AAA batteries so they get ‘properly’ charged as well as finding out the true capacity of the batteries but would like to get into using lithium cells/packs.

    BTW, the MAX1555 chip looks like a pretty good solution to safely charging individual lithium cells.

  10. I am pretty sure some of the usb monitored chargers
    out there can give you a capaicty test
    I can do it with this one as well be but it
    wont do the math it will discharge at a set rate
    and stop at the correct voltage and you can do the math after that it will keep the time and such displayed

    @lee the charger while cheeper is designed to do lithium with both safty cuts for time and capacity
    that can be set depending on the battery you choose to charger you can have upto 5 separate preprogrammed batteries saved or you can just change them for what ever you need when you need it

  11. At first I thought this was just going to be about replacing the cells inside a drill/tool battery, but I guess the point is about the individual cells inside the pack. I never really thought about doing a partial replacement, making new packs from old ones. At work we get a lot of these in to recycle… hmm…

  12. Ive got a Dyson handheld vacuum cleaner, and it only lets you have the power in 10 second bursts..
    the battery is obviously failing but i CBA to buy a specialist one.. should i just hack the old battery and replace it an old drill battery? or should the electrics be more complicated than that 

  13. Lee, I have grown a pair. Now I take care of them by trying not to burn them off.

    Another tip for people who extend this to laptop batteries: I took a very old laptop battery apart to figure out what cells it used and why it wouldn’t charge. I looked up all the parts on the charge circuit to work out what it did. What I was surprised to find is that the charging circuitry was powered by the batteries themselves. If the batteries depleted beyond a certain point, the charge circuit became inactive and there was no way (short of opening the pack) to get the module to charge. By trickle charging the cells directly (wall wart + 100R) up to about 6V I was able to get the laptop to resume charging duties. Of course the cells themselves were still shot so once the charger went away the pack died again.

    One further quirk which I never fully explored: The charging circuit had several parameters which could be programmed. The catch was that they were not retained in flash, just by virtue of — you guessed it — power from the batteries. So by the time the pack was dead, whatever parameters had been set were lost. This was an old NiMH pack so I’m not sure how critical they were. I can imagine a Li cell would be touchier.

  14. I have seen a couple of these types of articles featured around the web, but I have a project that I am not sure how to being. The idea is to take a relatively gutless Ryobi 18v chopsaw and convert a dead battery into a ac/dc converter for 110v. The ease of moving and size of the chopsaw are crucial, not the running off of batteries. Anyone seen a project for similar?

  15. @ben jackson this is pretty common.

    the main issue is the security algorithms used in the newer packs to prevent recharging *ever* once below some predefined threshold.

    its mostly for liability reasons, and also to enrich the pockets of the battery pack manufacturers.

    interestingly some newer laptops have a “charge to 80%” feature that extends battery life somewhat.

  16. “interestingly some newer laptops have a “charge to 80%” feature that extends battery life somewhat.”

    The life span of Lithium Ion batteries is notably dependent on the average state of charge (SOC) that they are kept at.

    This is due to inherent chemical reactions which internally degrade the battery over time. These reactions are accelerated by high SOC and at high temperatures.

    Thus Li-ion batteries tend to have short life spans in Laptops due mainly to this effect (and of course the high temperatures).

    Since many Laptops are frequently used and stored with the battery at or near 100% charged, quick degradation of the battery is common.

    The real question here is why haven’t options existed in hardware/software to provide more intelligent battery management for ALL Laptops and other portable devices???

    Just having the option to temporarily disable charging of the battery when a Laptop is being used for long periods of time from AC power would really help to extend the life of the battery. (and would be less annoying than removing the battery)

    Settings to allow for only partial charging/discharging of Laptop batteries are also a decent idea which could have and should have been implemented a long time ago.

    My 2 watt-hours worth…

  17. @octel – I thought that was a pretty good hack however I’d prefer to buy a pre-made device that ‘just works’.

    @polossatik – thanks, that’s the kind of thing I’m looking for but couldn’t see any details on the discharge part of the unit’s capabilities, can it calculate the capacity of the cell/pack?

  18. Re: the odd new cell. Both Pb-acid and NiCd sets can be “balanced”, the first by gassing “equalising” charge, the latter by cycling at very low currents. I *guess* that low rate cycling might also equalise Li cells.

    @Ben Jackson
    Over the past decade or two I have been encountering more and more gear of all sorts that has some sort of monkey-grip “gotcha” built in, and it is requiring ever more charity on my part to see this as dumb stupidity rather than a serious emerging ethical question.

    I do not think it is ethical to build in a “day after the warranty expires” logic bomb.

    I include in this placing disk batteries on PCB’s where they are known to leak and total the device.

    Roll on the Shame Page that names and shames every brand name that employes some form of self-destruct into their products. {spit!}

  19. @Roly

    Slow charging will not balance Li cells, as they cannot tolerate trickle charge. IIRC, trickle charging converts some of the lithium stored in the electrodes into metallic lithium, a very volatile (and explosive) substance.

    There is a reason why balancers are sold for Li packs.

  20. Lithium ions don’t have a trickle charge mode at all. They can’t be overcharged. It’s typically 4.3 volts per cell and that’s it. If you go over the limit, they will vent and burst into flames.

    That said, the simplest battery management is a shunt over the cell to prevent its voltage from ever rising over about 4.1-4.2 volts. Like a zener diode, or something with a sharper response if you like. It wastes a little energy on charging, but you can charge the whole pack in series with a “dumb” charger that outputs approximately 4.2*number-of-cells and has a current limiter to prevent overheating the cells. The shunt does get hot, however, as 4.2 volts at 1 A for example equals 4.2 Watts lost in the shunt when the cell is topped up.

    And of the .5 kWh pack: if that seems huge, just think that you need 40 of them to drive an electric car some 60-80 miles, and you’d actually need about 80 of them if you want to keep doing that 4-5 years down the road, because the range starts degrading from day 1. You really need about four times, or 160 of such packs so the car would really hold its rated range to a more common 10 year life cycle.

    So yeah, pure electric cars aren’t quite ready yet as far as the batteries go. That’s the main reason why the EV1 had to be so tiny and slim, and why they built the Tesla Roadster out of a Lotus Elise instead of a regular road car: their energy budget is so much lower so they need less batteries.

  21. Typically, the battery industry regards the EOL point of batteries at when they’ve lost 1/3 of their rated capacity. The Tesla Roadster for example uses standard cells that last for 700 – 1000 cycles (measured in total kWh) to that point, and have a shelf life of 6-8 years.

    At that point, the 53 kWh battery pack, assuming that all the cycles are used up and the battery is 8 years old, would have 23 kWh left in it for an optimistic estimate, and taking the offical rating of 250 Wh per mile, it would go 92 miles per charge, minus 20% for the safety buffers to get 73 mpc.

    Now, assuming the total use cycles is about 850, the total distance travelled would be 180 200 miles and the maximum average daily distance travelled can be no more than 61 miles.

    Imagine what it means for electric cars that are to be introduced to the market very soon, that plan to use about half the capacity of the Roadster in their battery packs, while using more energy to move than the Roadster.

    I wouldn’t buy one either.

  22. Of course the previous example is a very simple linear estimate, and to get a more accurate calculation, you’d have to do some nasty differential math since the actual effect of a “use cycle” on the battery depends on the state of wear on the battery at any given time etc.

    The effect is that the maximum driving range stays somewhat higher than of the linear estimate until the very end where you begin to need to charge the battery every night, and then both ways to work and back until it just collapses.

    That’s the reason for the -1/3 EOL estimate, because at that point, the battery starts to wear out faster and faster under constant use.

    I iterated the effect once however, and concluded that if you set a certain min/max distance, say 40 miles that you have to drive 5 days a week and you can do with no more, the linear model actually gives you a useful battery life within +10…+15% of what you should actually expect.

    And when I ran the model against the information on cars like the Mitsubishi MiEV, it concluded that the car is a brick after just 3 – 4 years, mostly because the battery replacement costs a large part of what a completely new car would.

  23. Einomies

    Tesla offer battery packs which are far cheaper than petrol mile for mile

    They aren’t for travelling salesmen – everyone knows. Their new model has a range of 300m.

    You have to factor in depreciation which is about a third of a petrol driven car or 1 petrol car = 3 electric cars. Less maintenance, no taxes etc

    You can replace the MIEV pack for about $4,000 which will take you as far as $7,000 – $14,000 worth of fuel!

    And finally LiPo4 prices are plummeting.

    Electric cars are the way to go.

    1. In another post, someone asked if there is any way to reset the control board if the batteries are good and the fuse is good but the charger won’t charge the board. Unfortunately, no. Makita may replace the battery if the charge count is low, say under 150. Otherwise you have to use an aftermarket charger which ignores the control board. The Tenergy TB6 will charge it, but slowly (and safely). There is a clone charger that looks like the Makita but isn’t, and I don’t think it reads the control board. Might be the best bet.

  24. There is a fatal design flaw in this battery. They run the control board from one cell pair, which will deep discharge the one cell and brick the battery over time. That is the most common failure of this battery. See the black wire and white wire? That’s the power tap for the control board. It would only take a shunt regulator to get power from the whole pack (say, 10K resistor and 6 diodes — that’s simple and cheap). Makita is getting crucified on Amazon reviews for these spurious failures. It’s sad, because the basic battery is great.

  25. hi there i have changed the cell in my makita battery pack and have successfully got it working again but it will not charge it says he hacked the charger aswell but i cant find how to go about this any help on getting it to charge would be grate

    1. I found a simple way to hack the charger!!! All you need is a working battery pack (for its working chip!) and two electrical wires. Open the charger, plug the 2 wires to the – and + plugs where the battery fits… There is one that has a black wire and the other as no wire.

      Then get those wires out the charger. and close the charger. I had to dig some holes on my charger to get those wires out.

      Finally, put the two wires you got out on the battery that you just fixed. Be careful to put the good wires on the good side of the battery. The green light flashes.

      Then put the working battery on the charger normally. The charger will think that there is only one battery, but the charger will charge both batteries.

      The bad thing is that you can’t use a battery while the other one charges. But the good thing is that you can use you’re broken battery again!!

    1. yes I found that the makita charger will reset the chip of the battery if you charge the pack first to 21v and put it on the makita charger plug and unplug the charger 2 or 3 times with the battery on. now it hast to be 21.0v if you put the battery to charge with 21.anything the battery will be ruined. I use one of those laptop charger that it was 19.5v to charge the pack to the 21.0v they have a regulator inside and they can be set to 21.0v . I recomend to replace all the cells on the battery pack not just the bad ones they are cheap laptop batterys on ebay most red cells are for little or slow descharge and the tools stop and go all the time just the flashlight and 1/4 inch impact works with it, green and blue cells are allmost all good

  26. The battery controller circuit is pretty tricky and brained with a micro-controller with firmware sitting in the embedded flash ram. Your best chance is to replace the bad cell in the pack before the 3rd strike. If you get the red-green flashing light, replace the expired cells with fresh ones before the PCB brick itself. Check out my blog at see if we can hack this together.

  27. For those who are still looking for the “aftermarket digital charger, ebay carries the IMAX B6AC. It will ignore the chip. A good explanation taken from the seller below:

    My new battery is dead already?

    As it stands testimony from the contact I have had states the battery does not last more than 50 – 60 charge cycles (if you are lucky!)

    Makita make some quality tools so don’t get me wrong but they have over-engineered this battery to the point it self-destructs.

    The battery is made up of two components a bank of Li-Ion cells and a Printed circuit board (PCB).

    The cells are self explanatory the purpose of the PCB in most Li-Ion batteries is to protect against overcharging, overheating and deep discharging all of which damage Li-Ion cells and can cause them to become hazardous.

    Makita have designed this battery with all these features plus more, there is a microchip which will monitor how many charge cycles the battery has had and constantly collect data from it. Futuristic stuff if a little over the top. The intelligent circuit will also detect a faulty battery and after 3 failed charging attempts it will disable the battery permanently. Now this is a safety first approach and if you look up the dangers of Li-ion batteries you will see why.

    Here is where it all goes wrong.

    The intelligent circuit inside the pack needs to be powered, and it draws its power from the very cells it is monitoring.

    The basic design flaw is that the circuit is wired to be powered by only one of the many cells in the pack. The PCB draws a constant although small current from that single cell. If the battery is not used for a few weeks then that cell will deep discharge causing a weak link in the bank of cells, the pack then fails in the charger.

    Now who is to know that if they try to charge the battery 3 times in this state they will permanently disable it? Human nature is think, why is it not charging let me try again.

    So if you use your tools every day you might have been lucky enough to have avoided this by charging them regularly.

    Most of the people will trow this batteries in recicling bin without knowing this batteries can work like new if you will use a intelligent Li-Io charger.

    I started to give a closer attention to Makita batteries and i can say from all faulty batteries which i opened,80% didn’t take a charge from original Makita charger because the voltage from one or more cell droped bellow limit….soon you will try one of this batteries on Makita charger it will reject the battery…if you try more then 3 times the PCB board will disable forever and this battery will never charge with any Makita charger.

    But it can charge with this inteligent Li-Io charger and the results will be more then satisfactory…why i’m saying this?…because this charger will monitor each cell any time(balance charger) and it will protect the cells against overcharging.

    In fact the original Makita charger IS NOT balance charger and this is one reason why since the voltage of one cell will drop bellow limit the Makita charger will mark this battery FAULTY.

    And now after this teory is time for practice:..i’m using almost every day this batteries and i can say i didn’t notice any diference between this and the ones charged with Makita charger.One of the picture will show the battery voltage after couple days after this battery was tested with running cordless drill.

    1. Tell me more on this IMAX B6AC charger. I have several bricked batteries and its worth a try. How do you wire it to the battery? What are the settings? I’d bet if you gave a detailed description, others would join along. Great tools, but that BL1830 battery sucks.

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