NiMH (Nickel-Metal Hydride) and NiZn (Nickel-Zinc) Batteries

NiMH (Nickel-Metal Hydride) and NiZn (Nickel-Zinc) Batteries

NiMH (Nickel-Metal Hydride) and NiZn (Nickel-Zinc) Batteries
NiMH (Nickel-Metal Hydride) and NiZn (Nickel-Zinc) Batteries


NiMH (Nickel-Metal Hydride)

NiMH (Nickel-Metal Hydride)
NiMH (Nickel-Metal Hydride)


Until the late 1990’s, NiCd’s were the only option for rechargeable batteries in household sizes,but their capability was terrible, and they contain toxic cadmium, which means they were assumed to be disposed of as hazardous waste, not in household garbage. Around the turn of the century we had been saved from this tyranny when NiMH’s became broadly accessible, offering triple the capability, and with non-hazardous materials, for roughly the same cost. As a result, NiCD’s have all but disappeared.


Where to Buy

I like Amazon for most products, because the prices are reduced and they stock everything. In the event you want them now then many grocery stores stock them (as well as Radio Shack), however the prices tend to be higher and the capacities lower then what you can get from more careful shopping. Eneloops are great, and I have a separate page where I pay my advocated brands (and which to prevent).


High-Drain Performance

Devices that need plenty of power Fast, like Digital cameras, are called high-drain. That is as opposed to Apparatus that simply sip the juice slowly, like clocks. NiMH work great in high-drain devices. Them, and even design their cameras to the lower voltage of the NiMH’s. An example of a battery that doesn’t operate well in high-drain apparatus is a Standard alkaline (although you will find premium alkalines like Duracell Ultra that Work fine in cameras, except they can’t be recharged)



AA capacities range 1200 to 2700 mAh. Beware of vague brands that guarantee higher Capacity–they usually deliver only a fraction of the label rating. (See My list of good and bad brands.) Also make certain to get a good Charger because some less expensive ones do not fill the batteries up completely. NiMH’s supposedly lose some of their capacity indefinitely if not used for long Periods of time.



Regular NiMH’s have the highest self-discharge rate of any type of battery (which means that they lose charge by simply sitting around, unused), however there are Low Self-Discharge (LSD) versions available (such as Sanyo eneloop). So when purchasing NiMH’s, you have to choose between longer shelf life and greater capacity. Should you burn through batteries quickly, get the normal NiMH’s so you can delight in

the bigger capacity. But if you go months before using up the battery’s capacity, go for LSD instead. The table at right shows the relationship between self-discharge and capability.

One nice thing about the LSD versions is that they come pre-charged. Normal NiMH’s must be charged prior to use.



NiMH’s are rated at 1.2V First voltage, which Can Be Lower compared to 1.5V that alkalines set out at first. This is generally not a problem, but it will imply that flashlights will be dimmer at first, and Devices that require 4 or more batteries may burn through the batteries really quickly or not operate in any way. Digital cameras) are designed to operate with the reduced 1.2V, so the reduced voltage is definitely not a problem there. If NiMH’s don’t Supply enough voltage for your device, contemplate NiZn’s, or blending NiMH and NiZn together, after viewing the warning about blending NiMH and NiZn in the same device.


Voltage Drop

Like the majority of other rechargeables, NiMH batteries maintain the majority of their voltage within the whole charge and then suddenly plummet. This contrasts with alkalines, which lose their capacity steadily. For this reason many digital devices that inform you how much battery life is abandoned have trouble reporting an accurate level for NiMH’s. The voltage is very like both a fully-charged battery and a nearly-spent battery. Some devices (like my GPS wristwatch) allow you to specify in the setup menu whether you’re using NiMH or alkalines, so that they can try to be more accurate with the battery-remaining indicator.



Overcharging can reduce cycle life (the number of times the battery can be charged). Smart chargers understand when the battery is full and stop charging. Dumb chargers operate on a timer and will almost always overcharge or don’t fill up the battery completely, and they usually actually don’t fill up C and D dimensions. Charging NiMH with older NiCd chargers is not suggested. Note that some wise chargers are better than others, also.

You’ll get more cycles by charging your NiMH’s if they’re only partially depleted rather than fully depleted. (Battery University) However because you can generally bill NiMH’s hundreds of times, it is probably not really worth worrying about, and you can just charge whenever you like. Even Cadex, that makes battery test equipment and therefore knows a lot about batteries, states that it’s hard to formulate more specific tips for charging. They do recommend draining down to 1.0V once every 3 months.

A perfect charge rate is most likely around 4-6 hours (to get empty to complete). Faster than this will work, but isn’t optimal. For slower charges, besides wasting time, there’s the risk that a wise charger will miss the cutoff signal that tells it to prevent charging.


Cycle Life

NiMH’s are good for Hundreds of charge cycles in theory, but overcharging and repeatedly running down the batteries all of the way can reduce cycle life. To prevent overcharging, utilize a smart charger that stops charging when the battery’s had enough. (See the chargers page for recommendations.) You will also get more cycles should you charge your batteries before they’re fully run down.

Newest ones are rated for 1500 and 1800 cycles, even though it might take years and Years for many users to get to even 1000 cycles.



If your battery no longer holds a charge or its Capacity is no longer useful, it is possible to easily recycle it at over 30,000 Places in U.S. & Canada such as Sears, Office Depot, Home Depot, Target, Wal-Mart, Best Buy, and others. Find the closest location to you Out of RBRC or even Earth911.


Memory Effect

While NiMH batteries allegedly do not suffer from the memory effect that NiCd batteries allegedly did, NiMH batteries do occasionally suddenly deliver substantially reduced capacity every cycle. This is easily fixed by a good charger that has a “Refresh” setting. (It drains the battery fully and then gives it a complete charge, occasionally repeating the procedure a few times or until potential no longer improves.)



  • Rechargeable
  • Works great in high-drain apparatus
  • They’ve replaced. Also not poisonous like NiCd’s.
  • Quite common, so it’s easy to find both Batteries and chargers



  • Low voltage of 1.2V means that economical (untrue) flashlights run dimmer, and devices requiring 4+ batteries Might run through batteries quickly, or not work at all.
  • Many manufacturers self-discharge to empty after only a few months of sitting around if you don’t use them. Make sure buy the Low Self-Discharge (LSD) version if you want long shelf-life.


NiZn (Nickel-Zinc)

NiZn (Nickel-Zinc)
NiZn (Nickel-Zinc)


NiZn’s were introduced by PowerGenix in 2009 as an alternative to NiMH’s. Their gimmick is they have a higher voltage, so they are a solution for devices in which the 1.2V of NiMH The higher voltage also means that flashes in cameras However, the higher Voltage could be both a blessing and a curse, together with the higher voltage burning out lights and sensitive electronics, as we’ll see below. Also, they Suffered reliability issues (again below). PowerGenix made them in just the AA size, and for just a year or two, and then stopped them, but there are several Off-brands available on Amazon, and a few Chinese manufacturers on eBay, at a Variety of dimensions. PowerGenix told me in June 2012 they were speaking to other companies about getting them take over manufacturing, but that’s the past I heard. It’s not clear if the newly-arrived Ultracell manufacturer is established on PowerGenix’s technology.



PowerGenix NiZn’s suffer with reliability problems. See below for my poor experience with capacity. Also, NLee reports that after buying four cells and placing them through 20-30 deep cycles (0.9V), two failed (reduced voltage and rapid Self-discharging), and the other two suffer from reduced capacity (80 percent of original). Many customers on Amazon report their batteries dying prematurely too. It seems that over-discharging NiZn’s can easily damage them. (NiMH’s are more tolerant of an over-discharge.)


High-Drain Performance

High-drain Apparatus are those which need lots of Electricity fast, such as digital cameras. That’s as opposed to devices that simply sip the juice slowly, like clocks. NiZn work great in high-drain Apparatus, if the voltage is not a problem. (See the Voltage segment under).


Capacity and Run Time

There are many reports of reliability problems, including my own experience, which kind of make any published specs about capacity moot. I used 9 for about a year (probably fewer than 10 cycles) in electric toothbrushes and electronic door locks. Seven of the nine (Star Trek Voyager reference unintentional) fell to just 45-150mAh in capacity, and the remaining two were 996 and 1298mAh. They should have been 2500mWh ÷ 1.65V = 1515mAh. NLee the Engineer says that after just a year, two of the 4 he purchased endured reduced capacity down to 80 percent of the initial, and the other two simply failed. The following discussion assumes that NiZn’s do not suffer reduced capacity early, although that’s probably not true.

NiZn’s give more, shorter, or quite equal run time; based on what device you use them in. Engadget said that they obtained 300-400 flashes from their camera flash unit using NiZn’s, averaging just 200-300 using NiMH’s, and Tom’s Guide said their NiZn’s ran a CD player for three times longer than NiMH’s. However, devices that don’t limit the input voltage (such as the majority of flashlights and electric toothbrushes, for instance) will run out quicker with NiZn’s, since while the device was running the lighting was burning brighter or so the engine was spinning faster. NiZn’s will make camera flashes recycle much faster, though burning through a great deal of flash shots immediately can fry the flash. Also, the NiZn might not give as numerous usable flashes as NiMH, because NiZn’s may start off using super-fast flash recycle times, but then get slower than NiMH. (Strobist quotes a user that stated NiZn’s got worse compared to NiMH following 50-75 shots, and too slow to use after 200 shots, compared to 400 shots for NiMH.)

That’s roughly half of the best NiMH’s. PowerGenix therefore recorded the shredder on its battery in mWh (total energy) instead of mAh, because total energy between battery types is much more similar, and PowerGenix states that’s a more apples-to-apples comparison. That’s debatable, from either side. It is true that the complete energy is the same, but again, if the device being used does not limit the voltage, the device will utilize the extra voltage and the NiZn will spend its electricity faster, or so the NiZn’s will provide less runtime. (And when the device does restrict the voltage, then there is no benefit to using NiZn’s in the first place, as the only reason you would use them instead of NiMH’s is in case you needed the extra voltage to start with.).



NiZn’s Possess the Highest initial voltage of any rechargeable battery. The nominal voltage is 1.65, which can be even higher than the 1.5V of alkalines. And fresh from this charger, the voltage is as high since 1.85V. (PowerGenix, PDF) The greater voltage can be both a blessing and a curse. The upside is that flashlights burn brighter, and battery life will generally be longer in high-drain devices. (Some LED lights limit the voltage, so in that case NiZn’s will not be brighter than 1.5 alkalines, but they will still be brighter than 1.2V NiMH’s.)

But there are downsides to the extra voltage. For lighting, the brighter light usually means that the bulbs will burn out faster, sometimes instantly. (Amazon review) For electronics, first understand that some devices have a voltage regulator (which restricts the max voltage coming from the batteries) along with a voltage shield (that shuts off the device in the event the battery input signal is too high). If your device doesn’t have one of them, and the gadget is quite sensitive to voltage, then the batteries may fry it. It’s tough to know if a specific device is a “fry”, “auto shut-off”, or “no difficulty” variety. The fewer batteries

that your device requires, the less likely you are to truly have a problem. A one-batery device is the least dangerous, two-batteries are a little more so, four batteries even more, and with 8+ batteries you are just asking for trouble. Powergenix mostly ignores this problem within their advertising and marketing stuff, so shame on them.

If you are concerned that NiZn’s could be too hot for your device, then NiMH would be A better bet. If NiMH does not supply enough voltage to your device, you can blend NiMH and NiZn collectively, after seeing the caution about mixing NiMH and NiZn in the same device.



Powergenix claims a self-discharge rate of 8% a month, but NLee the Engineer’s tests showed 13 percent per month, and Self-discharge signifies the bateries lose their Charge by just sitting around, unused. Contrary to NiMH’s, there is no low Self-discharge version available. If you use up and recharge your batteries quickly this won’t matter to you. But if you need longer shelf life, you’ll want to consider LSD NiMH instead.




  • Rechargeable
  • Works good in high-drain devices
  • Lasts more in some high-drain apparatus than NiMH’s
  • Greater voltage (1.65V+) makes lights Burn brighter (except some LED flashlights which govern the voltage)



  • The large voltage (1.65V) may burn out Lights quicker, fry some electronic equipment without a voltage regulator, and just Not operate in some electronics that don’t have voltage regulators
  • High self-discharge speed (they shed ~13% Of their first charge per month just sitting around)
  • Capacity plummets as the cells are Cycled (used & sterile)
  • Calls for a special, proprietary charger.
  • Potential reliability issues (high Failure speed: cells die fast or self-discharge even quicker than normal)
  • They’re ever-so-slightly bigger than Normal, so they might not fit in those rare devices where the batteries are already a tight match.
  • Semi-discontinued
  • Not available in any sizes besides AA and AAA
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