Recommendation for nimh AA cell

I have an application where I will use nimh AA cells at roughly 1C rate daily during part of the year. I have some cells now, but they are all old and don't perform as well as I would like. Low self discharge is nice, but not a requirement for my usage, as I expect to recharge them frequently due to use.

Looking for a quality cell recommendation. Low price is nice, but I would like them to last 5 years or so minimum.

sbslider said:

I have an application where I will use nimh AA cells at roughly 1C rate daily during part of the year. I have some cells now, but they are all old and don't perform as well as I would like. Low self discharge is nice, but not a requirement for my usage, as I expect to recharge them frequently due to use.

Looking for a quality cell recommendation. Low price is nice, but I would like them to last 5 years or so minimum.

Click to expand...

1C is 2A-2.5A, depending on whether it's a standard Eneloop/Fujitsu, or the hi-cap Eneloops/Fujitsu (or equivalents).

For longevity, I'd go with a standard Eneloop/Fujitsu NiMH AA, based on reported lower internal resistance over a 5 year span.

Chris

Thanks for the quick feedback. Best I can tell this light will demand 2,12A from fresh eneloops according to another user.

I wondered if non eneloops with more capacity would provide better performance.
In looking at this site: http://lygte-info.dk/review/batteries2012/CommonAAcomparator.php
and comparing eneloops to Duracell ultra 2400mAh cells the duracells provide higher voltage at 2A and a significantly longer (~25%) Ah to roughly 1.15V, where my light will start to drop step down in output to conserve battery. But I imagine the cells tested are all new, did not know that eneloop internal resistance would stay lower in the long run.

I can certainly see my 2650mAh Duracells are not perfroming too well. They are 10 years old, and sat unused for 9 years probably, so I am not complaining. But the voltage drop from 0.2A to 1A is 0.5V in a 4 cell stack, so I see they are individually dropping 0.1V+ each. The link above suggests I should see no more than 0.05V drop per cell with that current change. I am actually pleasently surprised they behave as well as they do.

On the other hand, 2 rather new eneloops and 2 unknown vintage eneloops drop 0.2V when the current changes from 0.2 to 1A, just like the graph predicts. And when the current doubles to 2A, I should expect another 0.05V drop per cell, which is very close to what I see.

The next situation to investigate is improving the electrical connection from the battery pack to the driver . . . At the 2A level the resistance here could really contribute to depleting the cells quickly.

Hi,

Well, 2.12A is definitely in the sweet spot for an Eneloop, standard or XX/Pro (or the similar Fujitsu standards and hi-caps) so I don't think that that's a problem. As you get to a lower state of charge at 2.12A, you'll start tanking rapidly, so it's not entirely linear.

The hi-caps will yield about 2.4Ah-2.5Ah, so you'll get about 25% more capacity out of them, but they start developing higher I.R.s in shorter order, so that might make 5 years more problematic.

When I started out here 5.5 years back, I revamped all of my 2000 era batteries and started buying up hi-cap HSDs like the Sanyo 2700s and AccuPower 2900s and they weren't really that close to the published numbers and were closer to the then spendier Eneloop XX 2500 LSDs.

The Sanyos were kaput in about 3 years, developing high I.R.s with moderate use and no real abuse. The AccuPowers lasted a bit longer, but suffered the same fate.

The Eneloop XX/Pros, the Fujitsu 2450s and even the Duracell Ion Core 2450s all get to that upper I.R. level faster than the standard LSDs, so keep that in mind. Still, these batteries are cheap to replace even every 6 months, so cost shouldn't be a big factor.

I'm no electronics whiz, so take my comments with a grain of salt.

Good luck, Chris

ChrisGarrett said:

I'm no electronics whiz, so take my comments with a grain of salt.

Good luck, Chris

Click to expand...

You might not be a whiz but I appreciate your real world experience, thanks for sharing.

sbslider said:

Looking for a quality cell recommendation. Low price is nice, but I would like them to last 5 years or so minimum.

Click to expand...

How many times a year do you recharge them roughly? On this it would depend how many cycles your batteries should really be able to achieve over the course of 5 years...

Hi sbslider,

my line of thoughts: IF the voltage of a charged battery = 1.4V AND the low voltage cut off of your light = 0.9V THEN the voltage drop on battery due to IR must not be higher than 0.5V. 500mV @ 2Amp => max IR = 250 mOhm

- standard Eneloop - 1800 mAh, 2100 mWh, 750 cycles till 250 mOhm - http://aacycler.com/battery/aa/panasonic-eneloop/
- IKEA LADDA - 2350 mAh, 2800 mWh, 170 cycles till 250 mOhm - http://aacycler.com/battery/aa/ikea-ladda-2450/
- Eneloop Pro - 2400 mAh, 2850 mWh, 130 cycles till 250 mOhm - http://aacycler.com/battery/aa/panasonic-eneloop-pro/

If you were to recharge your cells daily this is what I predict:

- cycles 0-100 (0-3 months) - Eneloop runtime 1 hour, LADDA/PRO runtime 1 hour 24 minutes. You love your LADDAs and PROs, you hate your Eneloops
- cycles 100-150 (3-6 months) - LADDA/PRO runtime dropped to Eneloop runtime. You wonder what happened to your LADDAs and PROs
- cycles 150-200 (6th month) - your LADDAs and PROs died. The standard Eneloops still perform as at day 1, still 1 hour runtime
- cycles 200-400 (6-12 months) - still 1 hour runtime
- cycles 400-550 (12-15 month) - runtime dropping to 50 minutes
- cycle 551 - your flashlight is stolen. You don't mind, because you are already considering buying a new one, with double the luminosity and half the current

Cheers,
AA Cycler

Kurt_Woloch said:

How many times a year do you recharge them roughly? On this it would depend how many cycles your batteries should really be able to achieve over the course of 5 years...

Click to expand...

My current plan is to recharge the batteries 3x a week 20 weeks a year, so roughly 60x a year. Will be used in a bike light during non daylight savings time part of the year.

AA Cycler said:

Hi sbslider,

my line of thoughts: IF the voltage of a charged battery = 1.4V AND the low voltage cut off of your light = 0.9V THEN the voltage drop on battery due to IR must not be higher than 0.5V. 500mV @ 2Amp => max IR = 250 mOhm

- standard Eneloop - 1800 mAh, 2100 mWh, 750 cycles till 250 mOhm - http://aacycler.com/battery/aa/panasonic-eneloop/
- IKEA LADDA - 2350 mAh, 2800 mWh, 170 cycles till 250 mOhm - http://aacycler.com/battery/aa/ikea-ladda-2450/
- Eneloop Pro - 2400 mAh, 2850 mWh, 130 cycles till 250 mOhm - http://aacycler.com/battery/aa/panasonic-eneloop-pro/

If you were to recharge your cells daily this is what I predict:

- cycles 0-100 (0-3 months) - Eneloop runtime 1 hour, LADDA/PRO runtime 1 hour 24 minutes. You love your LADDAs and PROs, you hate your Eneloops
- cycles 100-150 (3-6 months) - LADDA/PRO runtime dropped to Eneloop runtime. You wonder what happened to your LADDAs and PROs
- cycles 150-200 (6th month) - your LADDAs and PROs died. The standard Eneloops still perform as at day 1, still 1 hour runtime
- cycles 200-400 (6-12 months) - still 1 hour runtime
- cycles 400-550 (12-15 month) - runtime dropping to 50 minutes
- cycle 551 - your flashlight is stolen. You don't mind, because you are already considering buying a new one, with double the luminosity and half the current

Cheers,
AA Cycler

Click to expand...

Great response, thanks for sharing :twothumbs

The application is 4 in series, and best I can tell is the light (TN4A) starts to throttle back the output around 4.5V at the battery pack, or ~1.1 V / cell. So I am thinking below 100mOhm/cell would be ideal. Either way the eneloops win. I really like your data plots you linked to.

Minimizing the impedance between the cell carrier and the light is the next investigation.

sbslider said:

My current plan is to recharge the batteries 3x a week 20 weeks a year, so roughly 60x a year. Will be used in a bike light during non daylight savings time part of the year.

Click to expand...

OK, so we're looking at a requirement of at least 300 cycles. There are not so many cells that are able to do this, as you can see on this page:

http://www.aacycler.com/battery/aa/

In this case, for most of the cells, this is measured by discharging them to 0.9 volts and them charging them with a 0dv charging method, that is, the charging stops at the point where the voltage while charging would start to fall.

However, your case will probably be different, and it also depends on the charger you use and what it does to the batteries while charging... if it discharges them before recharging and how deeply it does, and on what condition it stops charging (if at all).

For instance, you can see the difference between different end points of charging here:

http://www.aacycler.com/battery/aa/panasonic-eneloop/

The cells with the grey and blue curves have been charged with 3mV -dV (which means they have to first lower the voltage by 3 mV below the peak before charging stops) and the brown one has been charged with 0dv. So, if the maximum acceptable internal resistance is 100 mOhms, the Eneloops would do 600 cycles when charged to 0dv, but only 350-400 cycles when charged to 3mV -dV.

However, if your light already drops its mode at 1.1 V or more, you probably won't discharge your cells that deeply (unless your charger does afterwards), so that would be easier on the cells.

But does it pay off to buy a charger that will do everything right? I'm actually not sure at the moment because, you know, chargers tend to fail as well, and I've read reports of Maha C9000 chargers, which are widely regarded as the "industry standard" for analyzing chargers, slowly losing one bay after another, although I didn't find any data on how many cells were actually charged in them before this happened. I just lost a Tronic charger which had charged only about 500 cells before it failed, but it was only € 8,99.

@AA Cycler: Since you have tested many cells on your chargers for many cycles, did you already have chargers fail? Or are there some that will do thousands of cycles?

I have Panasonic BQ-CC17 charger. I am not up on charger terminology, but this web page http://lygte-info.dk/review/Review Charger Panasonic BQ-CC17 UK.html says "A nice -dv/dt termination with only a small temperature increase and no trickle charge, this looks very good." Overall it seemed to be rated well, but slow. Slow if fine for me, I assumed it would improve battery life.

Yes, this one looks good in that it neither discharges nor overcharges the batteries and properly terminates the charge.

Just for the record, how long have you had this charger, and how many batteries has it already charged? (That is, how many cycles) I see this one is being sold (if it's still available) as a combo pack with Eneloop cells.

As for slow charging, generally it's better to charge the batteries slower. A faster charging rate doesn't do much harm during the main charge phase, but as the batteries get full, they heat up, and they heat up the more the faster the charge is. And the more they heat up while charging, the bigger the damage they take with each cycle. At least that's my understanding of things...

sbslider said:

I have Panasonic BQ-CC17 charger. I am not up on charger terminology, but this web page http://lygte-info.dk/review/Review Charger Panasonic BQ-CC17 UK.html says "A nice -dv/dt termination with only a small temperature increase and no trickle charge, this looks very good." Overall it seemed to be rated well, but slow. Slow if fine for me, I assumed it would improve battery life.

Click to expand...

Kurt_Woloch said:

Just for the record, how long have you had this charger, and how many batteries has it already charged?

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I bought it packaged with 4 AA eneloops back in March. When I bought it I did not have an interest in pursuing a different bike light setup than I have presently. I ended up selling two of the AA cells on 'the bay" to partially offset the cost of the package. I still have made in Japan 4 AA eneloop cells, two new white ones BK-3MCCA, and two I pulled out of a battery recycle bin. One is a dark blue sanyo HR-3UTGA, the other is a light blue panasonic BK-3MCCA. The light blue on fell out of a radio while I was riding my bike and is a bit scuffed up, but works like a champ still, even at the 2A my TN4A demands.

I would estimate I have charged but 40 or so cells with the BQ-CC17 on the AAA and AA rechargeable nihm cells I have in the past 5 months.

Kurt_Woloch said:

As for slow charging, generally it's better to charge the batteries slower. A faster charging rate doesn't do much harm during the main charge phase, but as the batteries get full, they heat up, and they heat up the more the faster the charge is. And the more they heat up while charging, the bigger the damage they take with each cycle. At least that's my understanding of things...

Click to expand...

When I charge 4 AAs in the charge they get pretty warm, but not uncomfortable to the touch. Based on the few times I have felt them during the charge it seems to only be at or near the end. I think the cells heating up is consistent with the end of charge.

Kurt_Woloch said:

@AA Cycler: Since you have tested many cells on your chargers for many cycles, did you already have chargers fail? Or are there some that will do thousands of cycles?

Click to expand...

I bought my first 2 MC3000s in March 2016, then 2 more units shortly after, and finally my last one 6 months later So I have 5 in total, 4 are used non-stop 24/7 doing battery cycling. I just calculated how many cycles they went thru that I published: 28982 1.5Amp cycles and 13642 0.5Amp cycles. If we divide by 4 we get an average of 7250 1.5Amp and 3400 0.5Amp cycles per unit. So all of them have gone thru 10000 cycles already.

So far I had only mechanical issues:
- the well known issue with the springs (4 of my units are affected, they are from the early batch). 3 springs snipped so far, 13 are to go
- I need to lubricate the fans every 6 months because I keep them busy and they go loud

So far there was no electronic failure, the 12V adapters hold up fine, the firmware is rock solid (I am on different versions, I upgrade only when I need to power the charged down, either for fan lube or spring fix)

Overall I like these MC3000 chargers. But for everyday use I prefer something smaller without fan, the mentioned BQ-CC17 for example, or the OPUS BT-C700 I use currently...