Decreasing AA NiMH Battery Cell Capacity!

Batteries and Chargers Rechargeable Batteries
1

I have four Energizer AA NiMH cells rated at 2300 mAh. Not entirely sure how old these cells are; maybe around 5 years??

I am wanting to maximize the capacity of these cells by running "cycle" mode on the charger. The charger should charge first, followed by discharge, and then repeat until the number of cycles has been completed.

Charge current set at 200 mA. Discharge current not adjustable when running in cycle mode, and discharge current defaults to 1000 mA.

I tested (cycled) just one of these Energizer cells first to see what the results would be before cycling the remaining three cells.

On first cycle, the discharge capacity for the single test cell was around 2163 mAh. Not bad!! But after the second cycle the discharge capacity had dropped dramatically to only 917 mAh!!?? And after the third cycle, the cell capacity dropped a bit again to 912 mAh!!??

There appears to be something wrong here as there should not be a dramatic drop in measured cell capacity so soon after each cycle!?

Note that all of the Energizer cells had some existing charge on them, and I didn't (manually) discharge the test cell first before starting the cycling process. Maybe because I didn't do a discharge first could have caused some issues with the charger cycling process?

I didn't monitor the charger cycling process continuously, I just checked progress every couple of hours or so.

I did note that the charging phase of cycling seemed to be relatively quick despite a low charge current of 200 mA. Certainly for the first cycle, the charge just topped up the existing cell charge, so a quick charge was to be expected. But for the subsequent second and third cycles, the cell should have been (near) fully discharged and I would have expected a longer charge time for these last cycles, but it didn't happen!

I'm wondering whether the test cell could be suffering from "capacity memory"? Although for NiMH cells, this "memory" issue is, according to various online sources, should be minimal to near non-existent.

Or is there an issue with the charger?

Or maybe issues with both the cell and the charger!?

Ideas?

2

On a refresh cycle the charger should put a fixed amount of charge into the battery relative to the nominal capacity of the battery, and ignore deltas.
Do you get to set the battery capacity anywhere, and how long is the charge cycle?

The discharge rate of 1000mA sounds too high, if the charge cycle is 5 hours (which is possible given the battery capacity measures just under 1000mA) is it possible that the 1000 refers to what the charger thinks that capacity of the battery is instead?

3

Battery capacity is not asked for by the charger. There isn't an option for setting this, unfortunately.

Yes, I'm not really happy with the discharge current of 1000 mA. Unfortunately this is not adjustable when cycling cells. I would have preferred something like 500 mA for the discharge current.

I didn't really note the time it took to do the charge part of the cycle, but it might have been somewhere around 3~4 hours at a very rough estimate!?

A bit earlier, I discharged the test cell manually on the charger with discharge current set at 500 mA. But the discharge capacity appeared to be only 84 mAh!!?? As I'm typing this, the test cell is presently being manually charged with a current set at 200 mA.

It should prove to be interesting to see what the final charge capacity becomes after this manual charge. Then I'll manually discharge the cell and check it's discharge capacity.

4

Try other slot, or other charger. This happend to me too. Don’t remember what charger.
Tried other (analysing) charger and everything was as it should be.

5

Energizer NiMh cells (metallic grey or shiny silver with green writing) have always been poor in my experience.

I have had best results with IKEA Ladda or Eneloops.

6

The initial test cycling was done on charger slot 3, I think. The present manual discharge and charging being done on slot 1 of the same charger.

I have a couple of other chargers that might be capable of doing cycling (or similar), but I'll see what comes of this manual discharging and charging first.

The Energizers in question have a silver finish with a bit of green stylized marking on them.

7

The first versions of Opus BT-C3100 have separate circuits for slots 1-4 and slots 2-3.

8

I forgot to mention that the charger I'm using at the present is a new iSDT C4 EVO which I had just recently received.

I am beginning to wonder whether there is something wrong with this charger?

9

Cell been sitting around unused for 5 years?

10

Is there even a point to running a “cycle” charge (aka repair mode) on NiMH batteries? I find that after every normal use/charge cycle the internal resistance goes up ever so slightly and I can only assume the usable capacity goes down a bit. I’d just assume a repair cycle would just cause even more life to be unnecessarily drained from an NiMH.

Rather than try to revive a substandard NiMH (Energizer), I just relegate its use to only low drain remotes or wireless mice. Then, purchase some IKEA LADDA or Eneloops (if you want to splurge).

I’ve pretty much recycled all my old Energizer NiMHs other than a few. Those remaining few are around 500mΩ (which is bad) and are only used in seldomly used remotes. All the recycled ones were above 1Ω internal resistance. My 7-year old Eneloops are still around 24mΩ.

11

I have wondered about the refresh cycle as well. Current charger does not have it. Charger that did sometimes missed termination and I think that did more damage than anything. 24mΩ on a 7 year old cell! All of my Eneloops wore out before then. I don’t think I’ve had a new cell that low. (Other than a 21700 and that is a whole different chemestry.) Do have a 10+ year old Energizer that has held up better than my Eneloops but I really don’t think that is a fair statement. It is an old cell but likely doesn’t have many cycles on it. However, my experience with the energizers, has been quite good.

In the end, a charger that misses termination probably induces more IR failure than anything, next is the number of cycles, and then somewhat blind luck. I know that everyone says how great Eneloops are and I know they are good cells. However, my experience with them is not much different than the energizers. Probably the worse cells I have were some Amazon Basics that were Made in Japan 2450 (Eneloop rejects?). They have retained their capacity pretty well but the IR is over 400mΩ. Work great for my thermostat and clocks but useless for a flashlight. Really high failure rate on those cells. However, I think the LaCrosse charger I was using at the time may very well have been the actual culprit and the brand of battery would not matter.

12

24mΩ was measured using an AC IR tester (which is probably lower than a DC IR test). I just tested using my Vapcell S4+, 7-yr Eneloop measures 50mΩ (using repeated tests and pushing the bottom slider hard for better contact).

I retested my old Energizer and it measures 245mΩ on Vapcell charger with DC IR and 765mΩ on AC IR (strange that it reads higher in this case with AC IR).

Your Eneloops that died early were they the white regular ones or the black pros? All mine are of the white variety (lower capacity but better IR and hold up better over time).

13

I don’t know that particular charger…but. Here’s a review of a previous model:
https://lygte-info.dk/review/Review%20Charger%20ISDT%20C4%20UK.html

[Conclusion

This charger has many functions and is easy to use, but it also has a few faults:
Auto recognition of LiIon 4.2V and 3.6V(LiFePO4) do not always work. I have seen 4.2V LiIon stopping at 3.6V and discharge/storage is also likely to fail if started with a partial full 4.2V LiIon.
First version of analysis missed the CV part, next version is better in that respect, but charger malfunctioned, this will probably be fixed in a later software update.
LiIon charge algorithm use way to high charge voltage, but the battery will not be overcharged.
There is also the limit on battery size, some common LiIon sizes requires spacers to be charged in this charger.

Do this charger match the top analyzing charger? The answer is no, it is far behind in settings and precision, but it is much easier to use.

For now I will only rate the charger acceptable.]

A comment/review on Amazon:
[The directions are of little use. Off/broken English and does not explain much. For example the ANALYZE function just says “This function is applied to the battery which is stored for more that 2 weeks or with weak discharge performance and this function could be also used to identify and match the battery capacity.,” (hell of a run-on sentence). That’s ALL it says about that!]

Maybe complicated to set up? The 200/charge and 1000/discharge are not appropriate: 1. You don’t understand how to set it up, or 2. It’s lousy for analyzing function if it produces automatic settings like that.
For a cycle of an unknown battery status of those cells I’d start with something like 700/charge and 350 discharge and see how it went, assuming you can do that.
If the 1000 discharge is ‘too much’ the discharge will terminate quickly. At 200 charge you may never terminate correctly. The combination will be a problem I think.
A decent NiMh AA will hold a 1A discharge just fine. When it no longer does, it’s on it’s way to the end.

Note - I have old Energizers like that that are still working after over 10 years. They aren’t great, but still work in low draw LED night lights and charge OK with the right settings.

There are VERY FEW NiMh that don’t have a pretty notable increase in IR after a bunch of cycles, age, neglect/abuse by users and inappropriate charger/setups. I’m in that camp, and the reason I ended up here to learn more. Still learning.

14

The ‘made in Japan’ Energizer 2300 batteries with silver mylar wrappers and green accenting and fiberboard washers have always been stellar in my experience and I’ve used them for almost 20 years.

They’ve brought some ChiCom versions out, so maybe that’s the problem?

Chris

15

Actually the four Energizers have been used on a few occasions in various devices but not used for over a year or so.

OK. The test cell stopped charging at only 919 mAh in the C4 EVO charger! Well below the cell's nominal capacity of 2300 mAh!

So this test cell is presently being run with "Discharge Refresh" mode using the Opus BT-C3100 V2.2 charger with current set at 500 mA. We'll see what happens here shortly.

The "Analyse" function for the C4 EVO charger was not used in my case here. I only used the "Cycle" function initially. By the way, the Analyse function uses a charge current of 1000 mA(!) by default and is NOT adjustable! This current is too high, especially for lower capacity cells (AAA size in particular) with nominal capacities around 600 mAh to 800 mAh!

16

The test Energizer cell @ 2300 mAh was tested in the Opus BT-C3100 V2.2 charger @ 500 mA and had a final discharge capacity of 2258 mAh. A good result! So the cell is not depleted or faulty.

Another Energizer 2300 mAh cell is presently being "cycled" in the iSDT C4 EVO charger @ 300 mA charging current; discharging current is defaulted to 1000 mA and is NOT adjustable when in "Cycle" mode, unfortunately.

At present this other cell is being charged properly by the C4 EVO charger @ 300 mA, and after two complete cycles, the cell discharge capacity is around 2200+ mAh. A pretty good result also!

So. It appears that if wanting to gently charge NiMH cells @ about 0.1C using the iSDT C4 EVO charger, the charge current should be set at 230 mA (for these Energizer 2300 mAh cells) at a minimum. But there is no current setting in the C4 EVO charger for 230 mA, the nearest settings being 200 mA and then 300 mA. Since the 200 mA charging setting resulted in the cells being undercharged, the 300 mA setting subsequently enabled full charging of the cells.

Rule of thumb for gentle charging of NiMH cells at 0.1C (using the iSDT C4 EVO charger)? Set charge current equal to or (a bit) greater than 0.1C, and NOT less than 0.1C!

I might do a mini review of this iSDT C4 EVO charger. It has quite a few functions and settings, but there are several settings that have to be either incorporated and/or modified.

17

This charger was highly incosistent in my test, i’d not trust any numbers or even use it. So far can’t see any confirmation it improved in time.