Is this Eneloop battery bad?

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ksio89
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Is this Eneloop battery bad?

I charged 4 6-year old Eneloop AAs (BK-3MCCA, min. 1900mAh, made in Japan) on my LiitoKala Li-500 (500mA current), and one of them apparently didn’t terminate the charge. The capacity and internal resistance values were much higher than the other 3 batteries, and even after 6 hours, it was still being charged. I freaked out and removed the battery right after taking the photo. These batteries have been always charged with a smart charger (Panasonic BQ-CC17, which came with these Eneloops), so I’d expect them to still be healthy.

I did a NOR test afterwards (250mA discharge current), and the values were as expected, but I forgot to take a picture: 1821mAh, 1.50V and 30 mR. Do you think this cell is already bad, or it might be a one-off problem?

bad one:

good ones:

Edited by: ksio89 on 07/29/2022 - 18:35
flydiver
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Older batteries have a higher tendency to miss termination as IR goes up. Doesn’t necessarily mean it’s a “bad” battery, but maybe a less “good” one. If your charge voltage is too low, that increases the probability. Use 500 minimum for AA, 700 and 1A are also fine. I wouldn’t go over that unless you have a pressing need to get it charged.

You can also have extra resistance on the battery and/or contacts. Clean both….then>
Mark the batteries, swap bay positions, and run another NOR cycle. See if you get the same results.

FWIW, I don’t put a lot of faith in the accuracy or reliability of slider chargers testing IR. You can do the same battery in the same bay multiple times and get way different results.
If that is indeed a 500 (not the 500S which I have no experience with), I have absolutely NO faith that NiMh IR is accurate. I’ve had 3, still have 2, and NONE of them work for NiMh IR. Otherwise, a decent charger.

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ksio89
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Thanks for the extensice reply. Good thinking on dirt possibly increasing IR, I will clean the terminals. I will also redo a NOR test on all batteries, swapping bays.

About the IR reading not being accurate, what baffles me more is the 2888mAh capacity. I don’t even know if 2000mAh (typical) can hold that amount of charge.

And about charge current, I always use 250mA for AAAs, and 500mA for AAs,in order to reduce heating, no need for hurry, as I usually charge cells overnight.

jon_slider
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ksio89 wrote:
I usually charge cells overnight.
500mA for 4 hours should be sufficient for those 2000mAh batteries.. any more is not going into the battery.. its being wasted as heat, is my guess

I think you did right by not running more than 6 hours. Was the battery unusually hot to the touch? That would be a big red flag.

overnight can be too much if the charger fails to terminate.. especially risky with LiIon..

suggest you consider a 4 hour timer to shut off power to the charger while you sleep.. fwiw, always safer to charge under supervision, not while sleeping..

flydiver
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ksio89 wrote:
Thanks for the extensice reply. Good thinking on dirt possibly increasing IR, I will clean the terminals. I will also redo a NOR test on all batteries, swapping bays.

About the IR reading not being accurate, what baffles me more is the 2888mAh capacity. I don’t even know if 2000mAh (typical) can hold that amount of charge.

And about charge current, I always use 250mA for AAAs, and 500mA for AAs,in order to reduce heating, no need for hurry, as I usually charge cells overnight.

If a battery does not terminate, it simply keeps charging, and that is reflected in the capacity shown on the charger. THAT’s why checking capacity by charging is not accurate. It can also terminate prematurely, resulting in a lower that normal capacity.
Your suspect battery did not stop charging, so it appears like the charger put way too much in it. All that extra was shed as heat. If you ONLY did a discharge on it afterward, you would not see the ‘excess’. You cannot “stuff” a battery.

Chargers use various mechanisms to terminate. If you go TOO slow, it does not terminate, keeps charging, and ultimately this may be more harmful that a higher charge rate. LSD particularly do not like overcharging. This should give you more info.
Snip below from this link: https://batteryuniversity.com/article/bu-408-charging-nickel-metal-hydride

[t is difficult, if not impossible, to slow charge a NiMH battery. At a C rate of 0.1C to 0.3C, the voltage and temperature profiles do not exhibit defined characteristics to trigger full-charge detection, and the charger must depend on a timer. Harmful overcharge can occur when charging partially or fully charged batteries, even if the battery remains cold.]
Note-they are referring to a smart charger that should terminate, NOT an old fashioned dumb charger that never stops. You…..could…..put a AA in the charger, set it to the lowest charge rate, and it might never stop until you stopped it.

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Bort
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Likely the charger missed the termination.

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