Makita 18v LXT Lithium-ion Battery Repair

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Introduction: Makita 18v LXT Lithium-ion Battery Repair

About: An IT Professio​nal from the West Midlands, with an interest in history, food, wine and all things technical​.

I have been a big fan of the Makita 18v LXT cordless tools for several years now. In most cases I rarely if ever use the corded tools they replaced, despite this there does seem to be a major week point, the batteries. Out of the eight batteries I have purchased over the years four have failed out side of the warranty period, plus two failed within or just after the end of the warranty and were replaced at no charge by Makita.

It seems there are two main failure causes, number one over heating and the second is the first two cells fail due to them being used to power the battery management chip and slowly discharging over an extended idol period. This causes the battery to be unbalanced. Once you get the red / green flashing lights three times on the charger your battery control board locks the battery from being recharge again.

I will be concentrating on replacing the battery control board as frequently this is all you need to do to get things up and running, although if you do require new cells these can be changed pretty easily. Makita seem to use the Sony Konion LiMn cells and these are available online for between fire and ten pounds each or you can frequently pick up failed batteries on ebay and cannibalise these for parts. If you do need to replace cells spot welding to the cells is the best way to go, as if you solder you risk overheating. Battery tab spot welders do come up on ebay from time to time or its something an electronics hobbyist could make themselves.

Step 1: Dismantling & Inspection

Before we start with the dismantling, remember that even if your batteries do not work anymore they most likely still contain a significant amount of energy. Be careful in how you handle them and above all make sure you do not short them out.

So the first step is to get the cover off. This is held on by four T10 Anti Tamper screws, on newer models there may be a white Anti Tamper plug covering one of the screws. I have found that the easiest way to remove it is to drive in a small wood screw and pull it out with a pair of pliers. Once you have the battery open being careful that the retaining clip spring does not fly away or short out the control board you should be able to see if there are any obvious major issues. The first time I open one of these batteries up I was surprised how much dust had made its way into the batteries, I soon learned to keep my charger away from dust and never to charge them on the floor!

If on opening you seen any visibly damaged cells you are going to have to replace them which is outside of the scope of this write up.

Step 2: Testing the Batteries.

I had four failed batteries, and checked the voltages of the batteries and cell pairs individually. I found the following:

  • Battery One: Fails to charge with a over temperature alert. Also the plastic at the side of the release button has bubbled. It is showing 7.99v across the whole battery which is way to low and 0.04v, 0v, 3.96v, 0.04v and 3.97v across each of the cell pairs respectively. Upon opening up the battery there is obvious damage to the second pair of cells.
  • Battery Two: Fails to charge with classic red / green flashing lights. It is 12.84v across the battery and 3.2v, 0v, 3.22v, 3.22v & 3.21v across each of the cell pairs respectively.
  • Battery Three: Fails to charge with classic red / green flashing lights. It is 15.54v across the battery and 0v, 3.89v, 3.89v, 3.89v & 3.89v across each of the cell pairs respectively.
  • Battery Four: Fails to charge with classic red / green flashing lights. It is 18.15v across the battery and 3.62v, 3.63v,3.6, 3.63 &3.62v across each of the cell pairs respectively.

By way of comparison a known good battery seems to measure around 20v when freshly charged.

So I decided that my best option to end up with an extra working battery was to change the board on Battery Four as its cells were all pretty close on voltage suggesting it was fairly evenly charged. Up until recently replacement circuit board were not available so once you had seen the red / green flashing lights three times your battery was bricked. However recently they have become available for a round £10 which is certainly much cheaper than a replacement battery.

Fixing the other batteries is going to be a little more challenging. Whist it is possible to solder cells together the heat required to solder them risks damaging the cells. Having investigated purchasing a battery tab spot welder I feel that is out of my budget but I may have a go at making a capacitor discharge one.

Step 3: Replacing the Control Board.

The control board came with ok instructions on how to fit but they don't explain everything, this may be because it can be used with all of the models of 18v LXT battery Makita have made. Providing you have a bit of common sense you should be ok.

So apart from the soldering you might expect you also have to cut away a lot plastic and that's assuming you are lucky like me and don't need to replace any cells. If you do spot welding to the cells is the best way to go, as if you solder you risk overheating.As I had previously got the battery pack out of the case the first thing to do was remove the existing pcb and cut away the plastic pcb support etc as per the instruction. I opted to cut the nickel contacts instead of desoldering. Fitting the pcb and soldering the wires to the contacts was simple although I had to break out my larger soldering iron. By far the hardest part was getting the covers back on this took a little fettling of the plastic to get it to fit.

Step 4: Putting It to the Test!

Next came the moment of truth, I put the battery on a charger and it charged. I then fully discharged the battery and once again recharged the battery and that also worked. Eight month on the battery is still preforming perfectly.

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    48 Comments

    0
    ErikaR
    ErikaR

    Question 3 months ago on Introduction

    I was wondering if I could get the specifications needed for the type of cells and the circuit board I need to get. I have googled searched and looked on Amazon for the cells and I keep getting regular batteries or cells that look squatty (possibly not right size) than what I see in videos I have looked up. I have Makita 18v batteries that I would like to fix for myself and my boss, but I am stuck on what items I actually need.
    Also, my battery collection includes 3.0ah, 5.0ah, and 6.0ah if that makes a difference. I have never done this before, but am wanting to learn and do it the right way.

    0
    High Voltage Fun
    High Voltage Fun

    Answer 3 months ago

    I would recommend salvaging good cells from other failed batteries. It is important that cells are identical to the originals. I would also point out this repair is only really a good idea for older 3ah batteries.

    0
    Snoopy2022
    Snoopy2022

    2 years ago

    Please everybody : Beware of circuit boards with only two connections (+18V , 0V) to the cells.
    In order to protect your battery, the BMS must absolutely be able to measure the voltages of all the 5 series blocks, as the makita BMS does. If not, overvoltage will happen, and if the temperature sensor isn't close to the cells overvolting, the battery will catch on fire.

    0
    Zuikkis
    Zuikkis

    Reply 9 months ago

    While you are absolutely correct, the part "as the makita BMS does" is wrong. Older Makita batteries have a BMS with only +18V, +3.6V and 0V connections. They measure the 3.6V line and it should be pretty close to 20% of 18V or battery is marked as failed. What's more, these batteries are not charged to 100% by Makita charger, max voltage is only about 20V so only about 4.0V per cell. Batteries with proper BMS are charged to 4.2V per cell.

    The white board in above pictures is genuine Makita, green is chinese replica. But they both have only +18V, +3.6V and 0V connections.

    Fitting a newer model "full BMS" to these older batteries is possible but might require cutting some plastic to make the larger pcb fit.

    0
    kenm6087
    kenm6087

    Question 10 months ago on Introduction

    I have 3 bl1850 makita batterys and the yellow clip that plugs Into tools etc has broken over time, is this part replaceable,has anyone came across this issue, will post few photos ,thanks

    0
    kenm6087
    kenm6087

    Answer 10 months ago

    Photo there of yellow clip broken , they break easily ,which is annoying, I've contacted makita and other company's and all have said this can't be fixed ,

    20210610_124623.jpg
    0
    High Voltage Fun
    High Voltage Fun

    Reply 10 months ago

    Couple of options really, either replace the whole control board or just get a battery with failed cells but a good connector and swap it over. I dont believe it can be purchased as a spare part. Good luck!

    0
    kenm6087
    kenm6087

    Reply 10 months ago

    Thanks

    0
    dgatz271
    dgatz271

    2 years ago

    Nice presentation.
    The Makita batteries that I have are only 1.5Ah. Are they worth messing with?
    There are 2-packs of 2.5Ah Lith-Ion batteries for $36.99 on eBay. (Hard to tell where they're made tho')
    When you say you've completely discharged the battery...how was this done?

    Does the DC18RA battery charger ever overcharge? Or does the circuity prevent that?

    0
    WBHenry
    WBHenry

    Question 4 years ago on Introduction

    I bought new Makita 18v 5.0ah batteries that fit fine on my charger but don't fit on my drill.
    Is there a fix?

    0
    ArronS10
    ArronS10

    Answer 3 years ago

    Just grab a sharp stanley knife, and trim
    Plastic on battery.

    0
    High Voltage Fun
    High Voltage Fun

    Answer 3 years ago

    Sorry, I dont think so. I would be interested in a work around if you know of one.

    0
    WBHenry
    WBHenry

    Question 4 years ago

    I bought new Makita 18v 5.0ah batteries that fit fine on my charger but don't fit on my BHP451 drill.
    Is there a fix?

    0
    ChrisJ301
    ChrisJ301

    Answer 3 years ago

    Yep you'll find there's a little plastic stopper (about 5mm x 12mm long) on the battery slide of your drill. I shaved mine off with a sharp 10mm chisel. Supposed to stop old tools being used with new batteries or vice versa but I've had no issues in 3 years of using them daily since.

    0
    darryl1940
    darryl1940

    Reply 3 years ago

    I had the same problem with mycordless angle grinder cut off the tabs Bingo works well I suppose makita would prefer you purchase the correct batteries

    0
    Robertwb70
    Robertwb70

    Reply 3 years ago

    Did the same to mine, no problems yet (been about 2 yrs now).

    0
    High Voltage Fun
    High Voltage Fun

    Answer 3 years ago

    Sorry, I dont think so. I would be interested in a work around if you know of one.

    0
    darryl1940
    darryl1940

    Question 3 years ago on Step 1

    where can I get a circuit board in Australia to suit a makita Li battery

    thanks Darryl

    0
    JózsefP
    JózsefP

    Question 3 years ago

    I will change the panel of my Makita 18V 3 A battery pack.
    I bought panel on E-Bay from China. But this panel is so as in Your pictures, and in my battery pack is other type. I think it's never.
    My question: in panel of Your pictures ( old panel ? ), where to solder the 4 cell outlets ( B1, B2, B3, B4 )
    Thanks!
    Jozef

    0
    High Voltage Fun
    High Voltage Fun

    Answer 3 years ago

    Hi Jozef,

    I am not exactly sure what you want to know. But if your battery is a latter generation battery you will will need a different control board.

    Cheers
    Stuart