NiCd vs NiMH Batteries Comparison And Differences Explained

When comparing the Nickel Cadmium to Nickel Metal Hydride battery we have to take certain things into the account.

First off they are both good batteries for the use they are meant for.

Yes one of them is not dangerous for the environment. The NiMH battery is not toxic like the NiCD. We will talk about this soon.

There is no best battery. There is only a match between what the battery can provide and what a user needs and that match can be made in heaven or someplace else where you wouldn’t want to visit.

You should understand both of these battery types in order to figure out which one will serve your purpose the best.

That is why in this NiCD vs NiMH battery comparison I will show the differences using graphs and explain what they are and why they matter to you.

However, you should know that the NiCd battery has lost the battle in a lot of fields to NiMH and other chemistries. It is slowly becoming a relic unless it is used for special purposes for which it is the best match. So you are most likely going to be looking at NiMH by the end of this comparison.

NiCD vs NiMH Battery Comparison

Now let’s see what the in-depth differences are. But before we do that let’s see the short and quick version of it.

Below the short version there will be much more detailed and filled with graphs version. Make sure you check it out as you will learn the most there.

Quick overview of the differences and comparison

ilustration of a Ni-Cd battery
  • 1000+ life cycle
  • Lower internal resistance
  • Robust
  • Low self-discharge
  • Handles tough temperature conditions
  • Cheaper (Sometimes)
  • Handles well high charge currents
  • Easy for the charger to detect the negative delta V
  • Highly toxic for the enviorment
  • Low energy density
  • Worse effects related to memory and voltage depression

VS

illustration of a Ni-MH battery
  • 1000+ life cycle (many brands offer even more today)
  • Low self-discharge (quality manufacturers only)
  • Higher energy density (up to 3x the NiCd)
  • Environmentally safe
  • Has better handling of memory and voltage depression issues
  • Cheap
  • A bit higher internal resistance
  • Not as robust
  • Not as good at handling extreme ambient temperatures
  • Doesn’t handle high charge currents as good as NiCd.
  • Harder for a charger to detect the negative delta V.

Nickel Cadmium is a battery chemistry that has been around for a really long time. We know it well as it has been researched well.

The NiCD batteries have a really long cycle life (they can be discharged and recharged more often), they can handle a high current discharge rate and they are rather cheap.

Unfortunately, they are also highly toxic to the environment. The cadmium in particular is very environmentally unfriendly but we will discuss this later in the article.

Additionally the Nickel Cadmium battery has a low energy density when compared to the modern solutions like NiMH, Li-ion and others.

Now let’s quickly see the NiMH.

The NiMH battery has a much higher energy density when compared to the NiCD. This means that it will be able to store more energy or more Ah.

But it has a lower discharge rate. This means that it is not capable of handling higher current loads like the NiCD is. This difference is probably insignificant for you but depending on your use case it could be.

Finally the NiMH is more environmentally friendly than NiCD as it doesn’t contain toxic metals.

Comparing the Energy densities

I will present the difference in energy densities of the Nickel Metal Hydride batteries and Nickel Cadmium based on the research that I have done. Keep in mind that there are different ways of improving any of the battery characteristics including this one.

Differences in cell manufacturing, shape, chemical additives, reduction in acceptable manufacturing flaws and hundreds of other factors can produce different results.

However, generally speaking and on average the results are as a lot of research shows.

The NiMH batteries have significantly higher energy density. Or more precisely, higher gravimetric energy density.

The unit for this metric is Wh/kg. The amount of watt hours per kilogram of battery mass.

Graph displaying the energy densities of NiMH and NiCd cells.
Graph displaying the difference in gravimetrical energy density expressed in Wh/kg. Data source: batteryuniversity.com

The Cycle life NiMH versus NiCD compared

This is where the NiCad battery takes the lead on paper but in the commercial setting, the number of Ni-MH cells that achieve similar or better results has been growing for a couple of years now.

Currently there are tens of successful brands offering NiMH cells that achieve excellent cycle life and take the lead here.

Just take a typical NiMH AA battery from Panasonic Eneloop. It can be recharged up to 2100 times. Ni-CD is slowly losing on this front as a leader.

However generally speaking, the NiCd does offer a higher life cycle if we exclude the top quality NiMH providers.

Lets see this compared on graphs.

Graph displaying the difference in life cycles
This graph displays life cycle differences shown in 100s. However, this is not always a real world commercial display. Should be taken with a grain of salt. Source of data: batteryuniversity.com
Graph showing cycle life comparison between NiCd and NiMH battery in commercial setting on AA cell examples
This graph shows the cycle life when comparing NiCd and NiMH on commercially available AA cells. Tenergy and Panasonic Eneloop are compared. This is just to show that there are real life examples where NiMH is way beter than NiCd when it comes to this metric. Source of data: Tenergy and Eneloop.

Discharge rate comparison

The NiCd batteries still hold their own when it comes to the discharge rate. These batteries can output a higher current than the NiMH, generally speaking. There are of course special Nickel-metal hydride batteries on the market that can handle much higher current output.

For this reason, Nickel-cadmium batteries are still widely used where a high current load is necessary. They are a very common choice for portable power tools and similar devices.

Graph displaying the difference of discharge rate between the NiCd and NiMH cells.
Graph presents the discharge rate comparison between NiCd and NiMH cells. Presented in C measurement. C current draw is equal to battery capacity so a battery that has 5000mAh capacity under 0.5C load would have a 2.5A of current drain. Data source: epectec.com

Internal resistance

The nickel cadmium battery has a lower internal resistance than the nickel metal hydride which is why the NiCd can be discharged with a higher current load.

This makes them the best choice for applications where a high surge in power is required either periodically or constantly. They do have their limits as anything else but they make an excellent choice for this purpose.

Graph showing the NiCd versus NiMH internal resistance comparison
Graph displays the internal resistance comparison of 6V battery packs of NiCd and NiMH. Data source: batteryuniversity.

Self discharge – Energy retention

The NiCD battery handles this one better. While there are exceptions in the commercial setting, the Ni-CD battery has better charge retention when stored in comparison to the NiMH.

The difference is usually not a deal breaker but depending on the battery manufacturer it can be. Some NiMHs lose their charge significantly faster than the NiCad cells.

Graph displaying self-discharge comparison.
Graph displaying self-discharge comparison between nickel cadmium and nickel metal hydride batteries at room temperature. Data presented in percentage loss per month.

The Memory effect and battery maintenance

You probably heard of the “memory effect” the NiCD batteries face. The Ni-CD batteries are much more prone to this issue than the Ni-MH.

However, the NiCD doesn’t necessarily need to experience this problem. This happens because of poor maintenance. NiCD simply requires regular full discharge and charge and most importantly a proper charger that doesn’t overcharge them.

That’s the way they work. This is problematic in certain settings and in those scenarios these batteries are a bad choice. Some people make a mistake and purchase a battery for the setting where this is troublesome or use improper chargers and then blame the chemistry of the battery instead of getting the right battery and a charger for the right job.

Now what is this so called memory effect in the first place?

Long story short: The “memory effect” is when your battery “forgets” what its true capacity and voltage are and it convinces itself that it has a lower capacity and voltage. That way you get a weaker battery. This happens mostly due to the voltage depression effect thanks to the poor battery chargers that overcharge the battery.

Now the long story: This is a very complex phenomenon that is not well understood by many battery enthusiasts. However, please don’t hate on me if you disagree here. I will present what I know based on my research and experience.

The true memory effect (Not likely to happen in real application scenarios)

Image of the sintered plate NiCd battery design.
An example of a sintered plate NiCd design.

The so called memory effect does exist but it is not what the NiCD or NiMH battery will experience if you happen to have a problem with it.

A true memory effect is related to NiCD battery (sintered-plate nickel-cadmium designs) and it happens when it is constantly being discharged to any specific percentage of its capacity and then fully recharged. This needs to be an ongoing problem. It won’t happen from a few cycles. There can be a slight variation in the discharge level from which it is charged back up but not more than 1-3%.

As you can see, it requires precision. You need to be very precise in order to induce a true memory effect.

If the battery is constantly being drained but to different percentages before being charged to its full capacity it cannot experience a real memory effect.

The true memory effect will cause the battery to “forget” its actual capacity.

Voltage depression – Often mistaken for the memory effect

There is however an effect that is very similar to the true memory effect that people often mistake for it. It is called voltage depression.

This effect occurs if the NiCD batteries are being overcharged. This causes the battery to lose its voltage capacity. You should use quality battery chargers and not chargers that continue to charge the batteries after they had been fully charged. There are special chargers that are designed for long term “trickle charging” but those must be identified by the manufacturer and you must place trust in a quality brand.

This problem is curable. But you must understand one thing. It must be applied for each individual cell of the battery.

AA batteries or more precisely AA cells are already individual cells but more complex battery packs need a cell specific approach.

In order to cure this problem, you need to simply completely discharge the cell and charge it to its maximum capacity. The keyword here is the cell. Don’t try to discharge to zero a battery pack because one of the individual cells may exhaust first and other cells will force current through it which will produce permanent damage.

A battery pack may have a power management system in place that will cut off the power once the battery drops down to about 1-1.1V. If you can’t access the individual cells you can also discharge the whole battery unit until the voltage drops down to 1V and then recharge it. That should also work in most cases.

NiCd vs NiMH charging

There are so many different chargers and they have a lot of different methods of detecting when is charging complete.

You shouldn’t use NiMH chargers for the NiCD batteries or the other way around. Sometimes this is possible but unless a charger clearly states that it can be used both ways it’s probably the best to stick to its original intended use.

NiCD and NiMH batteries are charged similarly but there are differences. NiMH battery charging requires a more sophisticated approach at detecting that a battery is charged while it is much easier for chargers to know when the NiCD reached its maximum capacity.

I am of course talking about high quality chargers that utilize advanced technologies like the following:

Negative Delta V (NDV)

This is one of the best ways a quality charger will figure out if the batteries are fully charged. It looks for a specific voltage drop that occurs after the cell has reached its capacity. It is easier to detect with NiCD batteries because they display a more sharp decline in voltage once the battery is full.

This works best with fast charging of 0.5C and higher for NiCD cells. These cells also provide the best charge efficiency with the fast 1C charging.

On another hand, the NiMH cells don’t exhibit a sharp negative delta V like the NiCd as they reach their capacity. Especially when charging at a slower rate like 0.3C or 0.5C. A high-quality charger that can properly charge NiMH should have electronic filtering in place. This filter should skip the noise and voltage fluctuations originating from the battery and the charger leaving the focus on the negative delta V.

Graph showing the voltage drop of NiCd cell when fully charged.
Graph shows the negative delta V drop in Nickel cadmium batteries. The drop is more prominent.
Graph displays a voltage drop in NiMH cells after they are fully charged.
Graph shows much less prominent voltage drop after the cell has been fully charged.

If you wish to learn more here is a great video by EEVblog. It is old but gold as they say.

Other methods of charge detection

Many quality chargers have fallback values detection. If the negative delta V is not apparent then a voltage plateau will kick in and advanced algorithms will stop the charge because it detects no change in voltage for a certain period. This can help when charging the NiMH with a low current.

The next good detection is delta temperature observed over delta time or dT/dt. This means that the charger is constantly checking the variations in temperature of the batteries. Once a specific rise in temperature happens over a short period of time the charger knows that the battery is full.

These other methods are less reliable than the negative delta V method which is the best.

Charge speed NiMH compared to NiCd

They are both similar here except that the NiCd tolerates really high charge speeds without much heat build up. However, there are specialized NiCd batteries that are designed for ultra-fast charging that can tolerate charge speeds that are way higher than of NiMH.

The NiMH will tolerate high currents too but will build up more heat. Many quality chargers solve this issue by charging at 1C speed for a limited period of time and then they let the battery cool a bit before proceeding with a lower current until the batteries are completely charged.

Environmental impact and the NiCd toxicity

image of a cadmium metal

NiCd battery has always had a serious problem with its toxicity and this remains the single biggest reason for not using this power source.

These batteries can have a substantial amount of cadmium metal in them. Up to 18% in certain cells. This is a heavy metal that is very toxic for the environment if it ends up in landfills. While recycling these batteries is possible and is being done they still pose a risk.

The EU banned the use of these batteries except in the case of medical use, emergency lighting and alarm systems. The use for power tools was allowed until 2016 when the EU directive prohibited the cadmium batteries in power tools.

One of the most common uses today of the nickel metal cadmium battery is precisely for power tools. These batteries got out-improved on almost all levels by lithium ion and NiMh batteries. But for the power tools, they still represent a cheap and robust solution. But not in the EU.

Not every country in the world has recycling ability for these batteries so using them hardly makes sense from this point of view. If they need to be sent overseas or by road to vast distances just to be recycled it is better to seek alternatives.

Nickel metal hydride battery is much more environmentally friendly as it doesn’t contain toxic materials like cadmium.

Operating temperature and working conditions

Another plus on the side of the nickel metal cadmium battery is its endurance in rough working conditions. It can handle high and low temperatures and vibration very well thus they also offer better resistance to impact.

The nickel metal hydride battery is by no means unable to work in tougher conditions but it is inferior to its predecessor.

Cost comparison

It is tough to directly compare the nickel metal cadmium battery to the nickel metal hydride type when it comes to their prices in the commercial setting.

There are so many brands offering varying cell and battery prices.

However, the NiCd seems to be the cheaper battery type only for certain uses. Especially if we take into account its robustness. If used where it is necessary it will be a more economical choice because it will outlast the NiMh and it will supply a higher discharge rating per dollar. This only makes sense if using these batteries for the use where such characteristics are necessary.

However, if we take into account a significantly lower energy density of the NiCd battery then we see that the NiMh battery offers a much higher usable capacity per dollar. This is almost universally the case when comparing commercial NiCd’s to NiMh’s regardless of the fact that the NiMh cell may be more expensive in some cases.

We also need to take into consideration the fact that NiCd cells of certain types are getting harder to obtain in the commercial setting. This increases their cost. Additionally in the USA, a recycling fee is included in the battery price which further increases their cost.

While a lot of sources claim that NiCd battery cells are the most economical choice I don’t think that most real world applications prove that to be the case. This is especially true for regular household battery consumers.

Conclusion

All things considered, the NiCd battery is ready to retire. It is an old timer that is still doing great in specific case scenarios where other battery chemistries are unable to offer the same results under specific economic and environmental conditions.

In other words, the use of NiCd makes sense only if you really have no other choice. This article compared it to NiMH specifically but the Li-ion, LiFePO4, lead acid and other chemistries in a lot of use scenarios blow NiCd out of the water and the NiMH too.

But NiMH still has its place today and has it firmly. It is not going away anytime soon in consumer electronics and especially in regular household batteries like AA, AAA, C, D and similar cells.

The nickel metal hydride battery is a clear winner in this comparison except in battery characteristics which usually don’t justify the NiCd use when we take the toxicity into account.

If the nickel cadmium cells weren’t as toxic they would still hold their own in the market even if they have lower capacity than the NiMH. But this is their biggest flaw which rightfully prompted them to retire from everyday use today.

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