I have a few Makita 18v power tools and recently one of the batteries packed it in or rather wouldn’t hold a charge. I wondered if I could recover any of the cells from the battery pack. It is an old 1.5Ah battery so has 5 lithium cells in series to give the nominal 18v
The pack itself was relatively easy to open, just needed a star shaped T10 bit and something to remove the plug (to stop you tampering with it).
Inside were the five 18650 Lithium cells and the battery management PCB, a quick voltage check on each cell showed at least one was good. the number means that the cells are 18mm in diameter and 65mm long - similar system to the button cells.
The voltages across the cells were 3.6v, 1.5v 1.5v, 0.9v and 0.6v I was hoping that I could rescue three cells.
As you can see I am using a small powerbank and a tiny 1A Lithium battery management board to charge the cell. Currently the cell has gone from 1.5v to 4.05v which is a fairly good sign.
BTW while I was operating on the battery I had a stainless steel bowl close at hand in case one of the cells burst into flames. Lithium cells can pack a lot of fiery punch.
If you can obtain replacement cells, that looks as though it could be a good project. I have done the same with AA sized battery packs of the NiMH variety and saved a lot of money. AA cell size seems to the size of choice for many appliance manufacturers and that really helps people like us with a flair for repair rather than dump.
You can buy Makita battery copies for peanuts on eBay, I don’t need any personally because I have two original 5Ah and one 1.5Ah batteries for my equipment.
I have charged up one of the 1.5v cells until the voltage got to 4.2v when the charger cut out which was a good sign and am charging the second. The charger controller chip gets pretty hot initially but not outrageously so. I am hopeful of getting at least two good lithium cells out of this.
A few weeks ago I threw away a couple of Nicad LED lights which I regret now because they would have been easy to modify to take a couple of lithium cells and management module.
The charge controllers were about $4 for five 1A charger modules on Ebay, they come with a variety of USB connectors I chose the micro B type because I have heaps of those particular cords.
They would be excellent for camera batteries etc save having chargers for different makes cluttering up the place. when they all do exactly the same job. That was why I originally bought them but they are handy for any lithium cell.
We have a big problem in the UK because batteries are not allowed to be sent via the postal system and independent carriers really know how to ramp their charges up, usually making an economical repair almost impossible.
Not sure, to me its a bit of a black art, it looks like a small BMS sitting on the battery pack which should have kept the discharge state across the cells constant, so, all the cells should have been in a same state, that’s just a guess.
I wouldn’t mess around with lithium batteries. Just by the new 5Ah ones if its an LTX unit. My impact driver and SDS drill have them in, I think they are only about £60.
That is what is supposed to happen but once a cell fails the whole battery can’t be charged properly but you are right these BMS for multi cell serial layout are a black art. However as individual cells or in parallel they are much easier to manage and there are plenty of cheap management boards available on ebay based on specific chips designed for this purpose.
All I need now is a board to prevent the cells being over discharged if I get a few of them working.
I have charged the three better cells and will check them in the morning to see if they hold a charge. Tomorrow i will attempt to charge the two very dodgy cells but if the three cells hold up I will be a very happy bunny.
The trouble with that though Spitty, is now all the cells will have the same state when originally assembled to form the battery pack. I recently bought 8 new so called Energiser NiMH and when I checked them all from opening the pack, only 7 were up to expectations. One was already in the state of failing and even with a charge, it would not hold it’s charge for more than 48hrs, so the complete pack of 8 had to be exchanged by the retailer as not of merchantable quality. The replacement pack was okay, but this just goes to show that quality control is a thing of the past for lower value items.
I agree, I watch a lot of the videos assembling high capacity Ebike Batteries and, each cell has to be checked for consistency, before assembly. In this application, once assembled, each cell is checkable (by Bluetooth) on an app, on your phone.
I am wondering if the Makita BMS board has failed? The other battery of the same capacity and bought at the same time is still going fine.
This morning, when I checked the two cells that showed 0.9v yesterday when still attached to the circuit board were each showing about 1.13v.
One of them is charging as I speak and is currently showing over 4v as it charges. However it is too early the say if it is OK.
The three cells charged yesterday were all over 4.1v this morning so they might be quite usable.
I read somewhere ages ago that lithium cells allowed to discharge to 1.5volts were often recoverable so it could well be that I now have three good lithium ion cells and perhaps four. Very pleased with that.
The eBay USB charging board has performed well it stopped charging at about 4.18volts and allowing that my meter is only a cheap one that is pretty good in my opinion.
