Naximum Acceptable Internal Resistance Values

Is there such a thing as maximum acceptable Internal Resistance?

I have some older AA batteries and they ALL show 127 milli-ohms of internal resistance.

Does that matter? Seems high.
Is their measured capacity the only thing that’s important regardless of the IR ?

Thanks

It mainly matters in high current draw applications. If you’re not trying to draw high Amps, then it should be fine, IMO.

How did you measure the IR, by the way? Most battery chargers/analyzers can’t be trusted with that value, IME.

Hello,
I got the resistance values from an AccuPower IQ338XL

Hi Zebretta,

you wrote “AA batteries” so I assume we are talking about NiMH here. I’ve got some numbers for those…

The maximum acceptable internal resistance depends on your needs. My rule of thumb for AA NiMH cells is:

  • up to 50 mOhm - can be considered brand new
  • between 50-100 mOhm - start loosing capacity slowly - still good for high drain apps (~ 1.5 Amp)
  • more than 100 - quick capacity loss - no good for high drain apps, still good for low drain apps (< 500 mA)

I consider RI a superb indicator of battery quality/age.

Cheers,
AA Cycler

Then you wrote “they ALL show 127 milli-ohms of internal resistance.”.

I had a similar experience with LiitoKala Lii-500. It showed OK values for LiIon, but almost always 45 mR for NiMH. Very rarely showed it less than 45 mR, even for brand new Eneloops.

I believe Lii-500 has either difficulties measuring Ri for NiMH, or caps the values to 45 mR. Having a limit is nothing unusual, even the fancy Xtar VP4 Plus Dragon has a 150 mOhm limit. This might be OK for lithium cells, but for NiMH I consider it way too low.

Now the question is - has your AccuPower IQ338XL a similar limit of 127 mOhm? What does it show for a brand new Eneloop?

I have a Liitokala 300 and it maxes out at 125 mR (whatever thats supposed to be)

127mohms on a aa nimh is lousy.
i suspect that is the units highest reading and your cells are in excess of that.
which means they are either bad or the test function is inaccurate.
new eneloops are around 20mohm on the dick smith esr.

Great point Cycler and thanks!
Now that you mention it, I can’t recall ever seeing a higher IR value than 127 so that might be the units limit.

I don’t have any eneloops

Probably correct.
When I run the IR test on the same battery on my Turnigy Accucel 6 charger I get >999mohm

127 seems to be the upper limit for the IQ338XL

I also have a batch of cheap 18650’s that say 6000mAh on them (…lol) but measure out at about 700-800mAh
Fortunately, they are only used in 1000 lumen flashlights.

Yeah, I’m not sure I’d trust the IR measurements on most of these inexpensive chargers. FYI, my Opus C2400 showed IR of around 70 mOhm on brand new AA Eneloops.

I’m of the opinion that the numbers are really just an approximation and to be used to get a general overview of the cells condition .
Seems to me my 13$ opus Bt C1000 has shown me mR numbers of like 500-600 on some bad nimh cells . I think the new chargers are great… but they obviously aren’t precision test equipment.

The resolution of IR measurements is naturally very corse if its voltage measurement is not super precise.
Fx if the charger measures IR by loading the battery with 100mA and the resulting IR should be 50 mOhm, the voltage drop to measure is only 5 mV. If the charger can only resolve voltage in whole mV, then it can only decide within 20 pct. ie. 5mV will calculate as 50 mOhm, 4 mV as 40mOhm and 6 mV as 60 mOhm.
In this case there will be 10 mOhm between possible readouts around 50 mOhm.

Any numbers on an appropriate internal resistance for NiMH AAAs? I have some old ones, some are 199 mΩ and some are as high as 386 mΩ. Measured with a UMS2.

95% of my AA and aaa nimh measure +/- 52 0n my litcat Lii500; it might be stuck on that value cause it has been run hard an put up wet for a # of years.

These bats range from cheap (fufly) to expensive (eneloop and fujitsu).

The Li-500 is useless for NiMh IR. Something messed up in the design. I’ve had 3, they all were that way.

For IR I no longer use a charger with slider. I’ve gone exclusively to ZB206+ battery tester which uses a 4-pin test mode for IR. I find it repeatable and believe it’s reasonably accurate. I’m not sure the scale is ‘absolute’ but it’s a repeatable measurement.
I also find this system far more repeatable and probably accurate than any charger for testing capacity. It depends on how fussy you want to be.

Using this I’ve gotten AA from 35-50 when new, 50-100+ at middle age, and all the way up to 600-900 when they generally get recycled. Charging, termination, and use becomes problematic. Gotten AAA up to 500, which is quite bad.
Small cells have inherently higher IR than larger cells.
My maximum? Anything over 500 is pretty suspect, except for very low drain devices (LED motion activated night lights). Much over 150-200 start not performing well in higher draw devices.

Occasionally I get a battery that the IR does not reflect the performance. IR will be ‘reasonable’ but it won’t charge properly, or work right. I suspect some kind of internal short maybe. Those get recycled too.

"Naximum Acceptable Internal Resistance Values"

Naximum is Maximum to the Nth degree.

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