Test many high drain batteries internal resistance

The internal resistance of the battery is an important parameter to measure the discharge performance of the battery.

Generally speaking, the lower the internal resistance of the battery is, the higher the discharge current of the battery is.

The resistance of the battery need professional instrument test, and the multimeter can only directly test the resistance of the uncharged metal

Here are some of the internal resistance tests for high drian batteries

Sony VTC5 (12.75mΩ)

Sony VTC4 (11.94mΩ)

Sony VTC5A (9.87mΩ)

Sony VTC6 (12.83mΩ)

LG HD4 (11.38mΩ)

Samsung 25R (12.74mΩ)

Samsung 20RM (12.72mΩ)

LG HG2 (13.89mΩ)

Samsung 30Q (12.78mΩ)

Thats a neet device there. I wonder if the internal resistance increases as the cell ages/gets used alot.

LG HE2 (12.77mΩ)

Sanyo UR18650NSX (13.01mΩ)

LG HB6 (11.18mΩ)

Samsung 35E (21.9mΩ)

LG HE4 (13.77mΩ)

LG HB2 (11.22mΩ)

Sanyo UR18650RX (11.66mΩ)

Samsung 48G (14.09mΩ)

Very neat, I did post a review of it: Test/review of Vapcell Internal Resistance Tester YR1030

I think they are taking advantage of the principle behind these equations.
BTW, sorry that my symbol for R-internal looks a lot like R-1

The circuit represents a Voltage source (cell) with it’s internal resistance hooked up to 2 different resistors, with 2 different current draws.
The value of each resistor is unknown, nor does it matter

What is measured is the voltage drop across R-1 and R-2, the load resistors, and the current thru them.
The equations show that the R-internal is calculated from the change in voltage drop divided by the change in current.

The value calculated does not depend on the values of the 2 load resistors
Instead of using 2 load resistors, they are using variable voltage and current, AC, and doing the math.

The reason why this is so good, I believe, is because any contact resistance would be part of the load resistance, and wouldn’t matter, because the resistance of the load resistor is not used in the calculation.
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No, as you can see in my review it uses AC and 4 terminal connection.
The AC also means the value will be lower than chargers measures, because they use DC.

The circuit I drew up would use 2 meters at the same time. One measuring current and one measuring voltage, for a total of 4 separate terminal connections.
I still think that is the principle behind what they are doing.

They are measuring current and voltage at the same time, but with AC you do not change current or even draw current (I checked this with an oscilloscope)

This is the standard way to measure internal resistance.

Samsung 30T (6.77mΩ)

Sanyo 20700B (13.66mΩ)

LG HB4(10.97mΩ)

LG HG6 (9.26mΩ)

Sanyo 20650A (9.58mΩ)

Sanyo 20700A (8.96mΩ)

Samsung 13BM (11.99mΩ)

LG HA4 (10.67mΩ)
LG HD2C (11.95mΩ)
LG MJ1 (30.4mΩ)
Samsung 15M (12.5mΩ)
Sanyo 18650GA (24.5mΩ)
Sanyo 18650SAX (11.93mΩ)
Sanyo 18650WX (12.31mΩ)
Sony 18650 VC7 (24.4mΩ)
Sony 18650 VTC4A (10.5mΩ)
And some rewarp brand batteries
Awt 18650 3000mah (12.88mΩ)
Ijoy 20700 new version (12.47mΩ)
Ijoy 26650 4200mah (10.35mΩ)
vapcell 18650 2000mah (7.16mΩ)
BUSBARS 18650 1750mah (10.24mΩ)
Mnke 26650 (13.93mΩ)
And some LiFeCoPO4 3.2V batteries
A123 26650M1A (6.24mΩ)
A123 26650M1B (5.21mΩ)
A123 18650M1A (15.22mΩ)
A123 AHR32113 (2.22mΩ)

nice device.
i need to get one.
the dick smith esr works well on batteries but lacks resolution on the very low end where it is most desired.

“They are measuring current and voltage at the same time”

Yes, I think what is being done is that AC is used and they are calculating the delta V and delta I at each sample point of the Sine Wave
No, the peak current will not change from cycle to cycle, but it would all along each cycle.

It could be that they are calculating the instantaneous change in voltage with respect to the instantaneous change in current along that sine wave. Dividing the 2 will give the internal resistance.

Now, who am I to say how they are actually doing it. All I am saying is that they are calculating the internal resistance based on the principles of my circuit and equations.

Yes, very nice indeed!
I want one too. $58 on AliExpress

As long as you circuit can measure AC only need to divide voltage with current, no need to use the DC formulas.
You can find it all in my article about resistance/impedance: Internal impedance of a battery

Pardon my ignorance, will the internal resistance measurement be affected if the battery is fully charged or fully drained?

I notice most of the cells above are measured with DC voltage at around 3.5-3.6v

Wow, that Samsung 21700 30T looks like it could deliver the highest current of any cell I’ve seen. I see articles saying it’s a Panny/Tesla 21700 competetor cell. Looking at the reviews, very impressive.

That 30T cost me a battery holder during test, my holder could not handle 50A

It will increase when the battery is close to empty.

Will the difference be significant for that same battery? (eg. measuring the same battery at 3.0v vs 3.6v vs 4.2v)
or will there be a big variance depending on the type/chemistry/age of the battery?

I saw the sudden cut out in the graph. 50A just wow. That explains it. Thanks for testing it though!