Instructables - Makita 18v LXT Lithium ion Battery-Repair

I have just had my Instructables on how to replace the control board on Makita Lithium-Ion batteries accepted  for there Tools Contest.  Please take a look by following the link below and vote by clicking on the vote tab on the right hand side if you wish!

Makita 18v LXT Lithium-ion Battery Repair

Makita 18v LXT Battery - Repair Eight Months On

This post is just a quick update.  Its been about eight months since I repaired my first Makita Li-lon batteries.  I have been careful to let repaired batteries to cool down fully before charging and where ever possible not to fully discharge them but so far there have been no failures of any of the repaired ones.  

I have however had a couple more batteries fail, as an experiment I sent them to the Makita Service Centre. Even though they were out of warranty, one by a couple of month and one by nearly a year, they sent me replacement within a couple of days at no charge.  I future this will be my first port of call and only if this fails will I attempt to repair them myself.

I do however have several failed battery packs that I had already taken apart with the intention of repair, so are not candidates for sending to Makita.  Due to being unable to source replacement control boards, i had put these to one side and had even concidered using the good cells for another project. Thankfully I once again have a supplier of them who has stock and have ordered several, so will soon be back repairing batteries.

Makita 18v LXT Battery - Repair

So as I mentioned in my previous post I have purchased a replacement control board from Ebay for my Makita 18v Li-Ion LXT batteries.  This weekend I finally had enough time to have go at fitting it and whilst it is not just a plug in affair I would say anyone with a multi meter and a half decent soldering iron should be able to do this.

I was lucky and had a battery that had ok cells but a faulty control board so I decided to try repairing this one first. 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.

Next came the moment of truth, I put the battery on a charger and it charged ok.  I then discharged the battery using my circular saw and once again recharged the battery and that also worked ok.  Needless to say I will need to let it go through a few more cycles before I am confident enough to call it a success but all in all things are looking good!

Makita 18v LXT Battery Dismantling & Testing

So I have four failed batteries and decided to find out what has gone wrong each of them.  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 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. I was surprised how much dust had made its way into the batteries.

Below is a description of the fault on each battery.

1. 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.
2. 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.
3. 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.
4. 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 think my best option to end up with an extra working battery is to use the board from Battery One and fit it to the cells and temp sensor from Battery Four.  Changing the board should be pretty simple it just requires de-soldering.  Fixing the other batteries is going to be a little more challenging. 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.

That still leaves the failed cells and whist it is possible to solder cells together the heat required to solder them risks damaging the cells. Having investigated purchasing a spot welder I feel that is out of my budget but I may have a go at making a capacitor discharge one.