Battery charge termination test

The LiIon charge specifications usual says that they must be charged to 4.20V +/-0.05V with termination at some specific current (Say 50mA), but how much do variation in these parameters affect the charge, i.e. the final capacity?

In this test I will charge the same battery with different charge parameters and then discharge it to check actual charged capacity.

To do this test I charged with voltages between 4.00 and 4.30 volt and termination currents between 10mA and 400mA, for a total of 7 different voltages and 6 currents. This many tests will put some wear on the battery for this reason both the first voltage and the last voltage is 4.20V, this brings the total number of tests to 48. All tests have been done with low voltage and low termination current first, then increasing current and high voltage last, i.e. the 4.30V run was the second last (The final run was the second 4.20V).

Two year old 18650 cell

For the first test I uses one of my old test cells: The Panasonic NCR18650A, i.e. a 3100mAh cell that has been used a lot.

This curve shows the charge parameters and the charged capacity.

Let’s first look at the 4.20V line (The yellow line). The color of the dots shows the termination current, there is two of each dot: one for the first run and one for the last run. These two sets of dots shows that I lost around 13mAh during the 48 test runs.

Capacity depending on charge voltage:

4.15V with 100mA termination gives 2602mAh or 90mAh less.

4.20V with 100mA termination gives 2694mAh/2681mAh, I use the first value as reference

4.25V with 100mA termination gives 2751mAh or 60mAh more.

The termination current will also affect the final result, at 4.2V we get:

10mA termination gives 2732mAh capacity or 40mAh more.

100mA termination gives 2694mAh capacity is used as reference.

400mA termination gives 2604mAh capacity or 90mAh less.

Measuring voltage after the charger has stopped will not show the charge voltage, but something lower. This chart here shows how much lower the voltage has dropped 5 second after the charger stopped. As can be seen it is depend on what current the charger terminates at (This is not surprising).

The voltage will drop some more over time, due to the many curves I had to do, I only waited 4 hours before measuring again. After this time both the termination current and the charge voltage will affect how much the voltage drops. Higher charge voltage will drop a bit more.

If a voltmeter shows 4.16 volt (4.20 with 0.04V drop) on this cell (After the 4 hours), the charger may have charged with 4.20V and 100mA termination current (Yellow dot).

How well do voltage reflect capacity in a LiIon cell? Usual very well, but you have to wait until the voltage has dropped. The blue dots (60 seconds after charge termination) are not very close to a line, with the red dots (4 hours after charge termination) the dots are much closer to a line, but not perfect.

New high current 18650 cell

This cell is much more sensitive to usage, it lost 85mAh during the testing.

Capacity depending on charge voltage:

4.15V with 100mA termination gives 2780mAh or up to 115mAh less.

4.20V with 100mA termination gives 2895mAh/2810mAh

4.25V with 100mA termination gives 2878mAh probably 30mAh-60mAh more.

The termination current will also affect the final result, but not very much, at 4.2V we get:

10mA termination gives 2921mAh capacity or 26mAh more.

100mA termination gives 2895mAh capacity is used as reference.

400mA termination gives 2857mAh capacity or 38mA less.

It takes some time before the voltage drops on this cell.

After 4 hours the voltage drop is about the same as for the old cell.

A slightly used 16340 cell

This cell has considerable lower capacity than 18650 cells and the 400mA termination is a very significant part of the capacity.

Some chargers do not lower termination current when charging small cells, how significant is this?

Capacity depending on charge voltage:

4.15V with 100mA termination gives 602mAh or up to 40mAh less.

4.20V with 100mA termination gives 642mAh/629mAh

4.25V with 100mA termination gives 652mAh probably 10mAh-20mAh more.

The termination current will also affect the final result, not very much in mAh, but significant compared to the total capacity, at 4.2V we get:

10mA termination gives 666mAh capacity or 24mAh more

100mA termination gives 642mAh capacity is used as reference.

400mA termination gives 582mAh capacity or 54mA less.

The high termination current gives a large voltage drop on this small cell.

After 4 hours the high termination currents has a very significant voltage drop.

The 4 hour curve is close to a line, i.e. the voltage is mostly settled here.

Conclusion

Generally I expect 18650 chargers to use a termination current in the 50mA to 100mA range, this usual match the datasheets for the cells, as can be seen here it do not make a charger unusable if it uses a higher termination current, but the capacity of the cell will be lower.

For smaller cells it is best with a termination current below 50mA to get the most capacity.

Another detail: If a voltmeter shows 4.20V on a cell a few hours after it has been charged, the charger is over charging the cell (It is nothing serious), all cells will drop in voltage.

Notes

My test lab do not have air-condition, this means the temperature can vary a bit. This may have affected the result slightly.

I uses Ah, to get mAh just move the decimal point 3 places. I.e. 2.9Ah is 2900mAh

All discharges where at 1A down to 2.8V

My charger do not charge LiIon to 4.2V, is it faulty?

Estimating remaning capacity in LiIon batteries

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

I started on this test long ago and was planning to do it on my regular battery test stations, but they where always busy. After I accumulated more test equipment I got time on some other (high precision) test station to do it.

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

That’s dedication. Excellent

- LEDs & Other Stuff -Ω- UI CheatSheets -So, what would be a more desirable voltmeter reading after a few hours?

JOKE: I wish my hours were also 80 minutes long, just like HKJ’s (3hours = 240min). Then I could do so much more…

BTW, nice work!

Cycle count tests of AA batteries - http://aacycler.com

I did fix that, but obvious it takes some time before everything is updated.

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

Thanks for the review.

One of the charts on here you shared w/ me b/4 its release about 10 days ago!

The PA18650 w/ the red and blue dots which was used to estimate my 0.05v loss when charging w/ the Opus compared to my Fenix ARE-C2!! ~ 100mAh loss!

Capo has connections.thanks HKJ,,,,,,,now I will study it more!

Solitude breeds contemplation which creates clarity. 7.3.2017Environment molds a person. Perseverance changes them. 3.4.2001WOLFDOGI assume the 30Q went through 42 cycles during the testing (7 voltage termination levels tested with 6 termination currents each). Is it possible the capacity reduction was due to the fact it was a new cell (compared to the old Panasonic that would be already degraded due to the cycling)? Also, could the high voltage of some of the tests have anything to do with it?`

48 cycles, 8 voltages, I did 4.20V twice.

The larger drop may be due to it being a new cell, but I do not know it.

I would expect the higher voltage to cause a bit extra degeneration, that was the reason I did them last.

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

Thanks for the testing HKJ its on point as always!

How much would this test change if the cell where abused more? Say at a higher discharge rate?

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That would wear the cell faster, but do not affect how much energy is filled into the cell during charge.

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

I sometimes get dizzy looking at a bunch of graphs, but those were indeed extremely interesting. Tons of work there…I don’t even want to know how long that took you. Thanks.

How to present the data and how much data to present is always an interesting challenge when doing my tests. I did try a couple of different charts and this was the best result. A table was completely out, it is mostly useless, except if you are in a spreadsheet and can visualize the numbers.

Most of the time was automated test time.

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

Thanks for a very insightful series of tests! I enjoyed reading it and if sb still did that it should be stickied.

djozz tests translucent S2+ gaskets available for free

This test has the answers for many common questions, I’m sure.

Thanks a lot!

Incredible job! Thanks from Italy (and I suppose also by the whole CPFItalia)

Sorry, I did not see you question before.

Usual a good reading would be between 4.15 and 4.19 volt. Look at the 4 hour voltage drop chart, somewhere between yellow and green dot (50mA-100mA) on the 4.2V yellow line.

For smaller cells you want to look between the blue and yellow dots (20mA-50mA).

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

Great test as usual, I would like to see the same test on nimh battery`s to see how end of charge voltage is related to capacity, like 1.39v vs 1.55v what is the capacity difference?

John.

SkyRC MC3000 – Maha C9000 – LaCrosse BC-900 – Floureon BT-C3100 V2.2 – Accumanger 10 and 20 -Thunder AC6 LiitoKala Lii-100 – Cozypony 24W Solar Panel – Soshine H4 – Soshine T2 – Soshine E4S

With NiMH it is not as such volt related, I did some test some time ago: http://lygte-info.dk/info/batteryChargingNiMH%20UK.html

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

So, am I right to conclude that on a 18650, and our high powered lights that draw 5amps, <1 minute of turbo use will negate the difference from a almost full charge of 4.15, to a full charge of 4.20…?

Thanks for the detailed test HKJ.

SkyRC MC3000 – Maha C9000 – LaCrosse BC-900 – Floureon BT-C3100 V2.2 – Accumanger 10 and 20 -Thunder AC6 LiitoKala Lii-100 – Cozypony 24W Solar Panel – Soshine H4 – Soshine T2 – Soshine E4S

1 minute at 5A is 60mAh used.

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

Interesting test. Do you know the internal resistance of the batteries you tested? It would be interesting to see the correlation between that and the voltage drop after 5 seconds for the different currents.

Sorry but no, in this test I just did charges/discharges, there was no analysis of internal resistance.

The 5 second drop probably matched the internal resistance fairly well (not perfect), but the 4 hour drop included a couple of slower chemical reactions.

The internal resistance probably changed during the test, i.e. it increased slightly.

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/