Review: Nickel-Zinc (Ni-Zn) Rechargeable Batteries and Charger

The Ni-MH rechargeable battery is the most common AA/AAA rechargeable battery chemistry. It took over as the superior technology both environmentally and technically compared to Ni-Cd. These cells provide a nominal 1.2v, but have improved over time to offer larger capacities and lower self discharge. In fact, when it comes to AA/AAA’s, my favourite has been the Sanyo Eneloops because of their extremely reliable and consistent performance (soon to be called Panasonic Eneloop following the acquisition of Sanyo’s battery division by Panasonic). The price is also reasonable, and their low self discharge rates are amazing. Having suffered through Energizer 2500mAh cells which were useless after about seven days rest, the Eneloop really turned the tables on the Ni-MH technology and the majority of the Ni-MH cells on the shelves tend to be low-self discharge versions in various names (e.g. Varta Ready2Use).

But aside from Ni-MH and Ni-Cd, there was another battery chemistry which was struggling for some attention – the Ni-Zn battery. The main claim of the Ni-Zn battery was a higher output voltage, often stated on batteries as 1.6v or 1.65v, which better matched the 1.5v of alkaline cells and would prolong runtime in voltage-sensitive electronics.

It is the same marketing strategy as used by Rechargeable Alkaline Manganese (RAM, Grandcell) batteries which boasted an “exact” 1.5v, although those suffered from very short cycle life (and I was convinced that some of them were merely repackaged disposable alkalines). Over time, they also grew higher in internal resistance making them unusuable in heavy draw devices, such as early digital cameras. Several of mine had leaked after about 15 or so cycles, by which point they were useless. None of these batteries even bothered advertising their capacity. Despite winning several technological accolades at the time, they fell out of favour quickly.

The Ni-Zn, by being much more similar to the Ni-Cd in nature, was supposed to provide the benefits of both worlds. As it turns out, I decided to give them a go almost a year ago, and here are my findings.

The Batteries

For my Ni-Zn adventure, I had to turn to eBay. As it turns out, no local retailers stock Ni-Zn, but there was a plentiful supply on eBay. For the AA’s, I opted for the better looking “branded” cells. These were the Powergenix 1.6v 2500mWh cells, Made in China.

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Despite Powergenix introducing it to the market in 2009, they exited the Ni-Zn consumer battery market merely a couple of years afterward. They continue to target their technology at hybrid vehicles, but I haven’t heard any interest at all. Regardless, apparently there was a lot of excess stock, or someone else decided to manufacture under the same name, which is how I ended up with these.

For the AAA’s, I went with the “unbranded” option, which was almost certainly a Chinese generic manufacturer. It’s interesting to see them actually bothering to manufacture these types of cells given many have not heard of it. This was rated at 1150mWh at 1.6v.

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The battery manufacturers plaster the cell capacity ratings in mWh as they claim that it’s unfair to label it in mAh. The reason is due to the higher cell nominal voltage, and mWh represents the cell’s energy content, rather than the cell’s current capacity (which needs to be multiplied by the nominal voltage to get the energy content).

However, it is trivial to convert it. Taking the voltage and energy given, we can do the conversions to compare them with the “regular” eneloop cells of today:

             mAh     mWh
AA Ni-Zn    1563    2500
AA Ni-MH    2000    2400
AAA Ni-Zn    719    1150
AAA Ni-MH    800     960

Keeping in mind that we’re not comparing with the largest capacity Ni-MH cells, the Ni-Zn batteries seem to be competitive on energy content – in both cases being rated superior.

The Charger

The charger supplied was a bundled charger. It is quite cheaply constructed, and features a single bi-colour LED for charge level indication.

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Unfortunately, I had opened it up before, so some of the data is missing on the rear label. The model number is HG-1206W, and it seems like there are multiple versions of this charger suitable for different chemistries.

DSC_8485Internally, the charger is constructed on a single piece of PCB, single sided. It seems there is a little attention paid to isolation as you can see from the milled groove in the PCB separating the high voltage from the low voltage. Many positions on the PCB are not populated – it seems that these are options which are used for different chemistries or DC power input charging.

Interestingly, there seems to be a current limiting polyfuse or similar at the bottom, and an LED which remains inside the case. I have a hunch that this LED provides the voltage reference for the charger, as the Ni-Zn love to be charged up to about 1.9v, and that’s coincidentally quite similar to the voltage drop across a red LED. How about that!

Nothing flashy about the components they used either, but the silkscreening seems to be rather non-conventional, and some holes aren’t even drilled!

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The underside of the PCB has solder resist and a smattering of surface mount components which seem rather unusual for a low-cost charger.

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A few more pictures of the PCB from different angles.

Lets just say, this charger gets quite hot in operation. The transformer on it is probably quite poorly wound or set as it buzzes quite audibly during charging. The circuit itself has really only two modes – charging or stopped. There’s a little hysteresis between the two, and so as the battery approaches full charge, the charger “alternates” between charging and stopped causing an irritating “bzzt-…-bzzt-…-bzzt-…” sort of noise.

Performance

I think the clearest indication of now useful Ni-Zn cells are is the fact that, after just under a year, all of my cells have hit the bin for one reason or another. Some of the blue AAA Ni-Zn decided to swell slightly on the negative pole, but all of them developed extremely high internal resistance and extremely high rates of self discharge. They would become pretty uselessly flat after only five days of rest, and wouldn’t handle any significant draw. This was only after 3-5 cycles.

Their internal resistance got so bad that charging took excessively long – and the phase where the charger alternates between charge-and-stopped continued for many hours. Some of the cells never lit the charger green, which implies they may have developed dendrites and internal shorts (which was, incidentally, a shortcoming of the Ni-Cd days).

The AA’s fared slightly better, but not much so. Barely 15 cycles in, all of them had such high internal resistance that the runtimes got quite low. Much lower than the equivalent Ni-MHs.

Did I see any increased run-times? Generally, I’d have to go with no. Even fresh out of the wrapping, most of my devices using AA’s and AAA’s are relatively newer devices and will work quite happily all the way down to 1V/cell (the “end point” for Ni-MH – alkaline cells are often rated down to 0.9V/cell). The argument that you need more voltage seems a bit of a fluff to me – the reason is that internal resistance comes into play as well.

The reason why many high draw digital cameras worked better on Ni-MH compared to Alkaline is the same reason why Ni-Zn just isn’t that useful. In high draw devices, while the Ni-MH cells provide a lower initial voltage, their lower internal resistance means that at heavy loads, the cell voltage drops less! They can maintain their ~1.2v even under heavy multi-ampere loads. Alkaline cells cannot do this, and neither does it seem Ni-Zn can. This means that their cell voltages may fall below 1v under heavy load even before they are empty.

For any appliance to be economical with batteries, they (as a rule) must be designed to work down to about 0.9-1V/cell. Anything higher and you will not see full utilization of even 1.5v dry cells (which they would be designed for, at the least, with most modern appliances designed for Ni-MH use as well).

Another reason for shorter run times comes from basic dumb appliances such as unregulated old flashlights and heating element based devices. These will see the higher voltage and consume more energy as a result – and also shorten their lifetimes.

The voltage of the Ni-Zn battery is misleading – most of them have 1.6v written on them, but they need about 1.9v to charge completely, and about 1.85v off the charger. Their higher voltage can and does cause problems for appliances especially when you have three or more in series. I managed to get smoke coming out of a few appliances and permanent damage with four in series – the excess voltage was too much. Use only two to three in series for best results.

The other thing is the voltage discharge curve drops sharply when the battery approaches about 1.5v. This means that devices with low-battery indication or reliance on cell voltage indications to fail miserably. This can mean that they fail to shut down gracefully or signal impending battery doom.

The best application I found for my Ni-Zn batteries (until they failed) was in my LED flashlights. Both regulated and non-regulated ones managed to stay in the bright mode for a little longer. The regulated ones I use might be a bit aggressive in their voltage-sensing regulators, and switch into a dim mode before completely discharging the Ni-MH cells. The unregulated ones dissipate more heat and energy due to the higher voltage, giving a better brightness but possibly at the cost of LED lifetime.

Aside from that, I saw no other great uses for them. My digital camera hated them – their internal resistance screws with the flash recharge and the power-downs prior to low-battery-warning left the lens in need of juice to retract itself. A battery operated glue gun and a flash unit which used four cells both managed to smoke to death.

Conclusion

While by no means a scientific and methodical exploration into the performance of Ni-Zn, I think it’s clear why they failed to gain favour. Their performance degraded quickly, and they suffer from the same bugbears as early Ni-MH cells – self discharge. Further to this, their energy density doesn’t match modern Ni-MH cells either, meaning less run time for devices which don’t care too much about voltage. You have to watch out for devices which aren’t aware of the voltage curve of the Ni-Zn cells, as they won’t have enough time to gracefully shut-down on low-battery conditions.

Worse still, if you’re planning to use them in devices with several cells in series, the added excess voltage may cause problems – overheating, to appliance damage. I’d keep it limited to two or three cells. The voltage rating is also a bit of a lie – they probably “chose” 1.6v and 1.65v to look closer to 1.5v, although the batteries often sit near 1.85v open circuit after charging and need about 1.9v to charge properly. The electrochemical potential is 1.73v.

The very much touted increased run-time proved to be very much a fallacy in my experience, and the eneloops win out virtually every time.

All in all, it wasn’t an expensive exercise, but it was one which was very much a disappointment. Try Ni-Zn at your own risk.

For more battery related goodness, there is an excellent comparison of chemistries at Michael Bluejay’s Battery Guide. There is also careful methodical testing of rechargeable batteries by Michael “The Doc” Hains.

About lui_gough

I'm a bit of a nut for electronics, computing, photography, radio, satellite and other technical hobbies. Click for more about me!
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10 Responses to Review: Nickel-Zinc (Ni-Zn) Rechargeable Batteries and Charger

  1. Emre says:

    Thank you for your detailed review. I was curious about Ni-Zn batteries. Now I got my answers, really useful article.
    After reading your comments, I decided not to use Ni-Zn batteries yet. I guess battery producers need to improve that battery technology or maybe it will never going to be popular and never be a standart battery system for electronic devices.

  2. Alain Knaff says:

    Thank you for this review.

    One question: For devices which need 4 batteries, is it possible to put in 2 NiMh, and 2 NiZn?

    Indeed, I’ve got several devices which don’t run on 4 NiMh (not _enough_ voltage), so mixing might be a solution… but elsewhere I’ve read that mixing different battery types might lead to bad things…

    • lui_gough says:

      I would not recommend mixing Ni-Mh and Ni-Zn mainly because the cells have different capacities. This will lead to the Ni-Zn being over-discharged at the end of the discharge, which will cause damage to the Ni-Zn batteries. This is because, while Ni-Zn and Ni-Mh have similar capacity on an energy basis, the Ni-Zn has to deliver a higher voltage, and thus delivers less current for the same amount of energy. Thus the Ni-Zn will run out first, and the Ni-Mh may continue to push it along until they get damaged.

      It could also cause relatively unstable voltage curves during depletion, which can cause incorrect indications of battery status on devices leading to no-warning shutdowns and malfunctions (possibly).

      Despite this, I still don’t recommend Ni-Zn cells based on my experiences with them. The higher terminal voltage can cause damage to appliances straight off the charger. I haven’t been able to get reliable long term performance out of them, and their internal resistance causes voltage drop when the load rises as well, which negates some of the benefit of the higher terminal voltage.

      – Gough

  3. Rob Kostecki says:

    A big unfortunate is that some devices refuse to work below 1.2V. I have a remote sensor for temperature station which stops working event though the battery still has 85% capacity (due to the drop in the batt voltage). I hoped NiZn would solve the challenge but following the article I will have to look into alternatives – possibly small AA LiIon with zener diod.

  4. Markus Hoffmann says:

    I disagree!

    Although the rechargeable battery market is one big mess in general there are still some gems. To give some positive examples: I am using Generation3 Panasonic AA NiMHs (2100mAh), Sanyo AA eneloops (2000mAh) and Turnigy AA/AAA LSD NiMHs (2200/800mAh) for several years now. Neither has let me down so far. Commonly any low discharge NiMH cell seems to be quite delivering these days. But that is not the point.

    I have also tried the Turnigy AA NiZns (1500mAh) because of the alkaline-like nominal voltage of 1.6V. They have replaced the eneloops in my aging digital still camera almost 2 years ago and are noticeably prolonging operating times. To the present day I have charged them merely 4 or 5 times but didn’t notice any degradation. Cell resistance in fact is slightly higher compared to a good quality NiMH. But that is of no consequences for a medium current application. I am looking forward to trying AAA NiZns in my cordless phone now.

    So, why is our experience that different?

    There is no question about the huge differences in rechargable battery quality. But we also need to consider the way cells are discharged and charged. No cell will forgive exhaustive discharge, as most cells won’t forgive excessive overcharging. The more sophisticated battery chemistry becomes the more sensitive cells are to this. When charging NiZn cells a CCCV regime needs to be observed where CC would be appreciated half the cell’s c rate (750mA for a 1500mAh cell) and CV being no more than 1.90V.

    Looking at the Charger shown in the review it is obvious to me, as an electronics design engineer, that this thing is the kind of a dysfunctional ulta low-cost design I always loved to hate. Missing closed loop regulation (which would require a modern smps control semiconductor or a standard controller / opto coupler) there is no way the charger can provide appropriate CCCV charging. Moreover the two cells seem to be charged in series using a weak balancing circuit instead of individual cell monitoring. Thus it is impossible to properly charge two differently discharged cells.

    It is very likely that this Charger did a mayor contribution to the bad experience with the NiZns reviewed. In contrast the Turnigy charger I use (google “4P80T-NiZn”) offers individually monitored true CCCV charging at just something like $6 unit cost. When looking for a battery charger I would always recommend to choose one capable of charging a single cell or more. This will immediately sort the junk out…

    • lui_gough says:

      Dear Markus,

      Thanks for your comments. As a late entrant to the Ni-Zn game, the only cells and chargers I had easy access to were the cheap Chinese rubbish. Just like their locally produced Ni-MH, the quality can vary quite significantly. The charger may have been part of my problems, but I think the cells were likely to be the bigger issue.

      It seems that your cells are of much better quality – especially because it comes from a brand very well respected amongst the hobby RC market (Turnigy). However, I don’t find the cost of Ni-Zn and the special handling requirements to be worth the hassle, and having >3 of them in series is likely to cause some damage to appliances not designed to handle the higher open circuit voltage.

      However, it is good to have a positive experience to share – thanks for taking the time for the insightful contribution.

      – Gough

  5. Markus Hoffmann says:

    In the meantime I was able to try AAA NiZns in my cordless. And guess what? It says “use rechargeable batteries” which totally makes sense since alkalines may leak when charged!

    And this means NiZn would most likely be rejected by any gadget providing a charging cradle. Unfortunately there is also no benefit using NiZns with ultra low power devices such as wall clocks or weather stations, since such devices typically use lossy voltage regulation or none at all.

    This said, the range of application for NiZn batteries becomes quite limited. I can understand people refusing to adopt…

  6. Kean Sakata says:

    Having burned through 40 AA Power Genix batteries I can say they are of limited use at best and poor replacements for higher voltage applications at worst. I still have 10 out of the 40 that have survived but have shelved them as their discharge curve makes them hard to work with.

    The battery usually starts out around 1.8V and drops quickly to 1.7-1.65V. The plateau range works until 1.5V then cliffs.If I don’t catch the battery BEFORE the cliff voltage then the battery is usually damaged. At 1.45V it usually will have permanently reduced capacity. If the battery is allowed to discharge to a voltage below that (1.4V to 1.1V) the battery will almost always not charge again.

    I eventually came up with a lame scheme of monitoring my device’s voltage via the internal battery monitor and PROACTIVELY replaced the discharged NiZn battery at a preset point (much higher than I would have with other batteries) in order to not damage the cell. This process actually worked as I was able to get at least 150 to 200 cycles out of the batteries.But if I forgot, then the battery was unforgiving and had to be tossed. Who swaps out a battery at 1.55V???

    The other thing that bothered me was the fully charged open circuit voltage of 1.8+ volts. Older devices like my HP 200LX (used 2 AA batteries) couldn’t handle the 3.7V the batteries produced and killed it immediately. DC to DC converters weren’t designed to have a very wide window of voltage range back then. Heaven forbid I try a two AA Xenon Maglight flashlight. It’s nice and bright for a few seconds and then poof…

    Even when it was working (using my proactive technique) the run times were 15 to 20 percent less than using the standard NiMH (back then the Rayovac IC3’s were my go to batteries) so my search for better AA/AAA still continues…

  7. tt says:

    I saw the Powergenix charger and their batteries all sold as a package for $5 at Big Lots once. I decided not to try them, so I never did. Now I’m glad I didn’t. The voltage curve is wrong as well. If you wait till the devices don’t work, the NIZN will be damaged while the NIMH will still work again. So I stayed with NIMH with it’s lower voltage. At least they are a little more reliable, though I have to avoid all Eneloop products in my ION 8000 Duracell charger (and their kin, Duracell AAA, Amazon Basics), though most brands will charge fine, though many brands are not well matched either.

  8. tt says:

    The only practical application I can think of for them is to use in battery packs with a BMS system. I don’t think the run time would be as good as lithium ion, though.

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