Naximum Acceptable Internal Resistance Values

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Zebretta
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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

Edited by: Zebretta on 12/29/2016 - 11:23
Pete7874
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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.

Zebretta
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Hello,
I got the resistance values from an AccuPower IQ338XL

AA Cycler
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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

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

AA Cycler
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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?

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

Bort
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AA Cycler wrote:
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)

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snakebite
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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.

Zebretta
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AA Cycler wrote:
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?

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

Zebretta
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snakebite wrote:
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.

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

Zebretta
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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.

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AA Cycler wrote:
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?


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.
Boaz
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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.

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sixty545
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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.