How to test a multi-cell Lithium Ion Battery?

[leehljp]

After Seeing Jim Frye's thread " https://www.sawdustzone.org/forum/di...ging-batteries ", I have been thinking about mine. I do have some that are about 12 -13 years old and a few do seem to have a shorter life than others, even though I don't notice it on my impact driver or cordless drill because I only use them for a few minutes at a time. But on things like my 12" chain saw or weed eater or a couple of other 18V tools, they are short lived but IF I put one of my newer batteries of the last 2 or 3 years, I get much more work done.

So the question is: How does one test a multi-cell lithium ion battery to know its real world viability?

I asked this question on Google, but it brought up people with volt meters that tests only the charge on a single cell. Not exactly what I was looking for.

One other thread said to take them apart and measure them a week after being charged! Again, not what I need.

Is there anything, way or instrument that will tell me the viability of the 18V battery as a whole? I would like to see the potential left in the whole battery. Something like an automotive battery load tester.

Thanks

[LCHIEN]

First of all some education. What we seek in batteries is charge capacity.
You say you want to know the potential of your battery, that is simply measured wth a voltmeter because potential is voltage. Correct words matter greatly in engineering!

So actually measuring capacity is not terribly difficult. Capacity is Amp hours or the more diminutive milliamp hours for small batteries.
Basically that is what we call more accurately charge capacity. Energy capacity is in watt hours, the product of voltage and amp hours, and is usually best applied to packs of multiple batteries while charge capacity is applied to single cells.

Charge capacity says that the cell or battery will deliver a fixed current for some amount of time before it runs out. Generally we have "running out" meaning the voltage falling below a terminal voltage where the tool doesn't work right anymore. A 2000 mAh (or 2Ah) cell can deliver 1 amp for 2 hours or .5 amps for 4 hours or 2 amps for 1 hours or 4 amps for half an hours. Note that each combination when multiplied comes out to 2.

In reality, cells generally achieve a large capacity when run at lower current levels. The difference can be considerable. And note that there are limitations to the maximum current a cell can put out because its voltage will be dropping due to to internal resistance causing loss.

So back to measuring now that we know what it is.
A classic way of measuring it to load the cell to a known current using what we call a constant current load. Usually This is NOT simply a resistor because the current changes as the battery voltage declines during use. However it might be acceptable to use a resistor with lithium cells because they have a relatively constant output voltage. once the load is applied to a fully charged battery, we start a timer and watch the voltage. Once the voltage falls below the termination voltage, we note the time and multiply it times the current and you have the amp hours capacity.

Its a bit more complex than a Multimeter... you have to have the constant current load (programmable preferably for testing at different currents) and a voltmeter and some kind of computer to read the meter and count the time and compare to the termination voltage.
More complex modes can use a fixed resistor and integrate the current measured during the discharge and calculate the area under the current-time curve as the capacity.

professional battery testing labs usually don't have one instrument that does this. THey have programmable loads (with constant resistance, constant current and other current modes) and system voltmeters, and a system controller which monitors a number of loads and batteries for simultaneous testing and produces plots that look like this along with a computed capacity value


Yeah I know these are for Alkalines.

Here is the plot for Lithiums

and alkaline vs NiMH

Clearly such lab instruments can be used to test capacity of single cells as well as battery packs of multiple cells.

I have some AA chargers that have charge and discharge functions, selectable charge and discharge currents, and can report mAh in or out or just applied to a partially charged cell.

I don't know of any off the shelf battery testers - they are a bit complex to really understand what you are measuring if you look at all the explaining I had to do above.

That said, a quick check on Amazon:

https://www.amazon.com/Digital-Battery-Capacity-Voltage-Controller/dp/B07RNPHJN6/ref=asc_df_B07RNPHJN6/?tag=hyprod-20&linkCode=df0&hvadid=366430786295&hvpos=&hvnetw=g&hvrand=11163504884644784136&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9027759&hvtargid=pla-800984124219&psc=1&tag=&ref=&adgrpid=75985294733&hvpone=&hvptwo=&hvadid=366430786295&hvpos=&hvnetw=g&hvrand=11163504884644784136&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9027759&hvtargid=pla-800984124219

But I don't see any that can actively measure cell or pack capacity by actual charge/discharge method.

.

[leehljp]

Amazon.com
https://www.amazon.com/Digital-Battery-Capacity-Voltage-Controller/dp/B07RNPHJN6/ref=asc_df_B07RNPHJN6/?tag=hyprod-20&linkCode=df0&hvadid=366430786295&hvpos=&hvnetw = g&hvrand=11163504884644784136&hvpone=&hvptwo=&hv qm t=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9027759&h v targid=pla-800984124219&psc=1&tag=&ref=&adgrpid=75985294733&h vpone=&hvptwo=&hvadid=366430786295&hvpos=&hvnetw=g &hvrand=11163504884644784136&hvqmt=&hvdev=c&hvd vcm dl=&hvlocint=&hvlocphy=9027759&hvtargid=pla-800984124219

Yes, I saw that one but it also says 2-7 cells; Ryobi 18Vs have 12 or more cells, so it makes me think it will not work correctly for Ryobi 18V.

I am not sure of the correct terminology, but I am looking for the term that determines how much life is left in it, not how much charge it will take to get "full".
For instance in an automobile 12V battery with 6 cells, one can determine its health with a load tester. My lap top computers in the past 10 to 15 years have all had an app that would tell of the computer's battery 'health" and how much actual charge it could take. My current 3 year old lap top will charge the battery to "full" but current "full" will only be at 85% of its new capacity.

What is the health state or max full charge capacity compared to when it was new?

This is not a new science. My 2009 Camry hybrid returned an alarm last fall when the entire hybrid battery (with 204 cells) hit a 60% of original capacity. I traded it off. The point is, the life/capacity of the battery as a single component had dropped to 60% of it original max capacity.

Computers tell us the batteries state in percentages; Cars do it too (when it gets to a certain amount).

But in reading your insights, there probably are instruments that can test 18-20V multi cells but it would be VERY expensive!

[LCHIEN]

If its 18 V NiMH pack then its going to have like 14 cells.
If its Li-ion, a 18 V pack will have no more than 6 cells.
But the problem with these testers is that you generally don't have access to the individual cells in the pack to connect the probes.

[leehljp]

Loring, Thanks, that is correct - 6 cells. My mind was thinking of a defective 40V that I just took apart because of a defective circuit board. Aging is taking its toll. Thanks. Glad to have an engineer to call upon.

[Jim Frye]

Don't know exactly, but I've had experience with 12 volt SLA/AGM batteries. Since these have multiple cells within the battery case, it's somewhat like tool battery in that there are more than a single cell to test. I have a Ryobi riding mower powered by four 12 volt batteries connected in series to make a 48 volt pack. When the SLA/AGM batteries age, the pack starts delivering shorter run times before a programed shutdown initiates. Ryobi's troubleshooting process is to separately charge each battery and then subject it to a load test with a battery load tester. The load tester places a specific draw on the battery and shows the voltage drop under load. The battery should be able to handle the maximum load for ten seconds before the voltage starts to drop off. 12 volt 100 ahr. load testers are rather inexpensive (neighbor bought one for $40). The local battery shop used a high quality, variable load tester to check mine and showed one of the four failing the test. Still no individual cell test. There must be a similar process for the lithium multi-cell packs. Ryobi's new 80 volt, 10 ahr. packs cost $899 each and have 100 individual cells. Wonder what the test procedure is for that one?