Testing capacity of power tool batteries - any ideas ?

HUGE range of batteries & accessories at www.batteryhookup.com 5% coupon "POWERWALLS"


Jan 16, 2019
I'm thinking into doing something to be able to test the capacity of power tool batteries like Milwaukee, DeWalt, Makita, etc.

Given that the modern batteries auto-lock when reaching minimal power level I only need to find a way drain them in order o measure capacity.

Are there any special testers for this kind of work ?

Any ideas, thoughts are welcomed.


Jan 7, 2017
If the contacts are two springs that hold onto a plate (slide style batteries) use a tab soldered to a wire and slip them in.
For the clip in style, a little more difficult.

If you have access to a 3D printer, you can print a holder for the batteries with the contacts. Then run wires to the regular testers with a dummy cell (3d printed) to hold the test probes.

There are testers for these batteries, but without having access to the scrap that the manufacturers use, gonna be hard to get some specifically designed for those.


Mar 2, 2019
If i understand you correctly with your auto lock.
I am speaking only for Hilti tools/battery's.
In all the tools of Hilti is a sort of diode in it, when the battery is going down in his V it will not be strong enough anymore to bypass the minimum required V border.
Testing those battery's with a discharger that have not the desired cut off will give you some problems.
As an example:
My batts/machines are all 22V, the machine will stop working when the V drops to 18.5.
If your discharger can be set to 5V to name something you mess up the cells.
So you need a specific cut off voltage.
There own internal bms does not do this, they don't protect against over discharge....
The same with deWalt i thought, will check on them this week.

For charging, the Hilti chargers only have a "stop" charging when a certain amount of V is reached, next to auto V sensing in case of 14.4 22 even up to 36V packs( i heard a rumour for 60v packs)

When taking a battery pack apart and replace the old for new cells, please do so with the V on the bms.
Some bms'es will stop working.

I am afraid that this is mandatory for most if not all tools

Yes i did my job to help 4 of my batteries to the recycler...
Hilti developed a own tester, it works with IR and a short time sort circuit, like those lead acid battery testers.
But this is my suspicion, they are really not willing to tell, and i am not going to buy one to open it up to satisfy my curiosity :cool:

I hope this was a bit helpful and possible some food for your thoughts.

With best regards Igor

Ps after those lessons, all my batts have new cells and even 1 whole amp more:cool::ROFLMAO::sneaky:


Jan 16, 2019
I managed to assimilate one of these:
View: https://www.youtube.com/watch?v=BeD8qUT4_LA

I can set the min V value to anything (using 15V now) and select the discharge current as long as I don't exceed the max power rating of the tester (150W).

So I can do fine and safe with tests at 6.5A discharge for all 18V batteries.
Tested a few, next I will have to figure out what actually is the cut-off voltage for various brands.
The power tool pack protections clearly don't allow full drain of the cells, probably due to the lower available current.