Does IR go higher as Voltage drops?

[klrman]

Got some protected 18650 Keeppowers today (NCR18650GA) and they came in the mail at 3.5V. I have 12 of the same battery purchased over a year and all the others read around 85IR on my SkyRC MC3000. These ones read around 135IR. Haven't put them on the charger yet, but could IR be higher when the Voltage is lower?

[Mark_M]

Keep in mind it is giving you the resistance value of the entire circuit not just the battery. So there are many factors at play. It is better to test internal battery resistance with seperate equipment. Many people test with dc load testing or to a lesser extent a 1000 hz ac impedance test. You can also use a 4 probe ohmmeter. My charger gives me whacky numbers if the battery isn’t seated perfectly at insertion.

[klrman]

I know, but these new batch of batteries seem a little wacky. With the 1000hz ac impedance test, I get 20% higher IR readings than all my other 12 batteries which are the same make and model. Something doesn't add up with these ones I think.

[Barkuti]

Internal resistance of a modern li-ion cell generally stays flat over the entire discharge curve it is said, though I can clearly see the value goes down as the discharge curves approach the end of discharge point for the higher rates, this is due to cell heating. Check HKJ's comparator.

The properly named 1KHz AC impedance test is not that useful for our purposes, except to keep track of battery health. Wether the protection circuit messes up with the AC reading I don't know.

Do not measure 1KHz AC impedance with fully charged batteries on analyzing chargers, it won't work because no headroom for measurement.

Cheers ^:)

[Nooner]

Have you tried cleaning the contacts? I once received brand new Samsung 30Q button tops (for a reliable seller) and the IR measurement was extremely high. After a light scuff with sand paper and cleaned with alcohol they showed typical IR for that cell.

I was surprised that was the problem.

[klrman]

@Nooner

Have you tried cleaning the contacts? I once received brand new Samsung 30Q button tops (for a reliable seller) and the IR measurement was extremely high. After a light scuff with sand paper and cleaned with alcohol they showed typical IR for that cell. I was surprised that was the problem.

Yes, didn't make any difference.

[klrman]

@Barkuti

Internal resistance of a modern li-ion cell generally stays flat over the entire discharge curve it is said, though I can clearly see the value goes down as the discharge curves approach the end of discharge point for the higher rates, this is due to cell heating. Check HKJ's comparator.

The properly named 1KHz AC impedance test is not that useful for our purposes, except to keep track of battery health. Wether the protection circuit messes up with the AC reading I don't know.

Do not measure 1KHz AC impedance with fully charged batteries on analyzing chargers, it won't work because no headroom for measurement.

Cheers ^:)

That's the thing, it was not fully charged when I tested it with the SM8124A, but this afternoon I found the data sheet for the battery and it says <60 for the 1KHz AC impedance test is ok, so I guess it is ok then. Just seems a little odd that my SkyRC using the DC test shows double the IR compared to all my other batteries of the same part number. Batteries weigh almost the same and look legit. Any idea what should be maximun IR for the DC test before I should consider recycling batteries?

[Barkuti]

@klrman

… Any idea what should be maximun IR for the DC test before I should consider recycling batteries?

Normal DC internal resistance value is slightly below 80mΩ for such cell, see KeepPower P1835J HKJ's review:

Worn out/oxidized contacts can be extremely burdensome with resistance.

^:)

[klrman]

Thanks for the link and chart Barkuti That means something is up with these batteries. My other twelve P1835J batteries are all below 80 mΩ. Not sure what to do? Maybe I should talk to Keeppower first before contacting Bangood and see what they say.