How NiMH Batteries Work

NiMH is a rechargeable battery that is made to address operating issues found in older rechargeable batteries. In case you are not familiar with it, the name means Nickel Metal Hydride. The battery has plenty of advantages over NiCd’s and older battery types, and one of them is its memory effect bypass feature.

What is Memory Effect Anyway?
Batteries from older generations, including NiCd (nickel-cadmium), go through what is commonly called the memory effect, which can be easily demonstrated up by requiring these batteries to be fully drained before charging. Failure to drain these batteries before charging will result to reduced capacity. NiMH batteries are safe from this effect and can be charged anytime and at any point of their usage cycle.

Increased Battery Capacity
With the increasing demand for higher energy reserves, NiMH batteries are climbing up the popularity ranks fast. This is because NiMH has higher energy reserves that traditional rechargeable batteries. As a matter of fact, these new generation batteries have two to three times the capacity of a similar-sized Nickel-cadmium battery. Also, the density of its reserved energy is even comparable to that of a Li-ion battery.

Materials Used
To get a grip on How NiMH Batteries Work, it’s good to start with the materials used in making them. Just like your usual battery, NiMH has two metal strips that act as its positive and negative terminals together with an insulator placed in-between them; they are compressed and placed into a canister that contains liquid electrolyte. Now, this is where it become different from other batteries. The positive terminal is made of nickel while the opposite terminal is made of hydride, hence, the name.

Electricity Generation
When using a NiMH battery, electrons go out of the positive terminal, which then produces hydrogen. As this happens, the electrons go to the negative terminal as they absorb the hydrogen. The whole process produces electricity, which is put into reversed once that battery is put into the charger.

What Happens When NiMH Batteries Are Overcharged?
As mentioned, you won’t have to worry that much about “memory effect” with nickel metal hydride batteries but you will still have to worry about “voltage depression.” In case you haven’t heard of it, it is when a battery discharges faster than it should be. This is caused by overcharging a battery repeatedly. Repeated overcharging causes electrolyte crystals to form on the battery’s plates, which clogs the plates resulting to increased resistance and lower battery voltage.

Fortunately, voltage depression is not much of a problem. All you need to do is keep your NiMH batteries from overcharging to be able to use them at their full capacity. And since new generation NiMH cells don’t have memory effect problems, you can consider them to be low maintenance rechargeable batteries.

Trickle Charging
If you are worried about overcharging your batteries then you might want to use a trickle charger. Unlike your average battery charger, trickle chargers use low current to power up batteries. According to manufacturers, overcharging is nothing to worry about if you’re charging your NiMH at low currents. So, if you want to charge your batteries without dealing with overcharging then trickle charging is for you.

On Using Fast Chargers
When using fast chargers, you might want to be a little cautious about leaving your battery while being charged or you’d risk overcharging it. To be on the safe side, terminate the charging cycle right before the battery reaches its peak capacity. On the other hand, you can also monitor the charging process by observing the change in voltage and charging time.

Safety Feature
NiMH batteries feature a fuse installed in series with the cells the increases safety. The fuse opens up the voltage series if the current gets too high or the battery itself gets too hot. It can also be reset once activated, which can help increase usability.

Handling NiMH Batteries
If you want to increase the life of your NiMH then you should do the following:

– Avoid overcharging. Using a good charger can help you out with this.

-Store your batteries in a cool dry place. Storing batteries in hot and wet places can either decrease its capacity and lifespan or render them useless.

-Get high-quality NiMH batteries. Not all NiMH batteries are made equal; some are better than the others. High-quality NiMH batteries will give you your time and money’s worth.

If you’re looking for a battery that has great capacity, reliable energy reserve that doesn’t unexpectedly drain, and low maintenance requirement then Nickel Metal Hydride is for you. With improvements made in its newer generations, NiMH can be considered a groundbreaking rechargeable battery.

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The History of NiMH Batteries


The name NiMH is actually an abbreviation which stands for Nickel-metal hydride battery. It is a type of rechargeable battery. The distinct characteristics of a NiMH in terms of energy density, nominal cell voltage, charge/discharge efficiency, energy density and cell durability are as shown below:

Nominal cell voltage-1.2 volts

Energy Density-140-300 Wh/l

Specific power-250-1000 w/kg

Charge/discharge efficiency-66%(varies with temperature)

Cell durability-500-2000 cycles

The History of NiMH Batteries

The NiMH battery evolved from the nickel hydrogen battery which was used in aerospace applications. Since they have an exceptional cycle life and a favorable specific energy, they were used for aerospace applications for a long time before they were introduced to commercial uses.

Scientists started working on NiMH batteries in 1967 at the Battelle-Geneva Research Center. The basis of the work was scientists discovering that some metal alloys actually had the ability to store atomic hydrogen which is amazingly 1000 times their own volume. The metal hybrids are hybrids which were based on compounds such as LiNi5 or ZrNi2.Development was catalyzed by Daimler-Benz and Volkswagen AG. It was done by Deutsche in Automobilegesellschaft(a Daimler AG subsidiary)At the time, the battery specific energy was 50 W.h/kg while the specific power was up to 1000/kg.The cell durability was 500 charge cycles.

Sample applications were filed in countries in Europe (Mostly in Switzerland), The United states and Japan. They were later taken to Daimler Beinz and further to other parts of the world.

In the 1970s nickel-hydrogen used for satellite applications was commercialized thus interest in NiMH grew rapidly. Since the hybrid technology was not bulky in terms of storing hydrogen, it provided a better alternative. Philips Laboratories and France’s CNRS carried out research and developed new high-energy hybrid alloys which incorporated earth metals. These were used in the negative electrode. Sadly, they suffered from alloy instability in alkaline electrolyte thus causing insufficient cycle life.

In 1987, Buschow and Willems corrected the above error by using a mixture of La0.8 Nd0.2 Ni2.5 Co2.4 Si0.1.The battery now kept 84% charge capacity even after 4000 charge-discharge cycles which was a massive improvement. Viable alloys which used mischmetal in place of lanthanum were later developed. They were more economical.NiMH being used today are based on this design.

The first NiMH Cells were released to consumers in 1989.However, Ovonic Battery Company which was based in Michigan changed and improved the structure of Ti-Ni alloy and composition. The changes made included inclusion of special alloys which had a disordered alloy structure. Specific multi component alloys were also added. Unfortunately, the cycle life of the alloys remained low due to their composition.

For household sizes until the late 1980’s, the NiCd’s were the only available option for rechargeable batteries .However, their capacity was not good and they also contained toxic cadmium thus were supposed to be disposed as waste and not in household pits for health purposes. The NiCd’s were replaced by the NiMH which offered triple the capacity of NiCd’s and contained materials which were not hazardous. They both costed around the same price. As a result, NiMH became popular and the NiCd’s disappeared.

A high energy electrode which was developed by Dr.Masahiko Octane (GS Yuasa Company) led to the NiMH cell.The technology was further used in 2008 as more than 2 million hybrid vehicles were manufactured with NiMH batteries worldwide. At this stage the batteries were advanced hence their use in hybrid vehicles. The batteries were more portable for consumer use. Due to this factor, the European Union recommended that Ni-CD be replaced by the more effective and efficient nickel-metal hybride batteries. Statistics in Japan show that approximately 22% of portable rechargeable batteries were sold in 2010.As we can see, the batteries were proving to be efficient and effective. On the other side in Switzerland 60% were sold in 2009.Currently, Lithium-ion batteries are replacing the NiMH batteries though the NiMH batteries are still very popular.

In 2015. Germany’s BASF has made a step forward by producing a modified micro-structure which has helped to make NiMH batteries last longer. This has allowed changes to the design of the cell thus saving weight.It has also helped to increase the gravimetric energy density to 140 watt hours per kilogram. The NiMH battery technology is pervasive today and powers everything from hybrid electric vehicles to cellular phones, clocks, digital cameras etc.