The Ultimate Guide for NiMH Battery

Are you looking for a safer nickel-cadmium battery replacement? Nickel-Metal Hydride cells are perfect for that. 

Get to know the advantages, limitations, and different features of NiMH Batteries in this guide. You will also learn their differences from other rechargeable power storage.

Read and learn more!

What is NiMH Battery?

Nickel-Metal Hydride(NiMH) batteries are among the rechargeable battery variations. They have negative electrodes created from hydrogen-absorbing alloys. The cells also come with various inter-metallic elements. On the other hand, NiMH cell-positive electrodes are formed using nickel-oxide hydroxide compounds. 

NiMH Charging Methods

Charging NiMH batteries is possible in numerous ways. However, finding the best charger is a factor. Therefore, it is necessary to be aware of a proper procedure to avoid overcharging the batteries. Along with its advantages, each charging process has a disadvantage that needs to be considered. 

Time Charging

The most straightforward approach is timing. Time is used to decide when to stop charging. And typically, the charger has an electronic timer. However, this technique can be applied if the battery is in a known state of charge—for example, entirely discharged. 

Disadvantage: The charger will indicate an “overcharge” when a cell doesn’t charge. But this can accelerate the breakdown even more.

NVD Method

The negative delta voltage is preferred method for determining when charging should stop. This method is fit for charging NiMH batteries. 

Disadvantage:The technique can identify a decrease in voltage as the cell reaches its maximum charge. However, it will only detect a slight drop in voltage in NiMH.

Thermal detection

Another method for determining when charging is complete is to utilize the cell temperature.

Disadvantage: Since the cell’s interior is far hotter than its exterior, it will be challenging to determine the charging level accurately. 

Charging Precautions

Here are some essential overviews of valuable recommendations for NiMH battery charging methods.

  • Charging at a suitable ambient temperature of around 20 °C
  • Utilize the correct charger to recharge the cell. It’s because inappropriate chargers will create unstable charging. 
  • Examining the temperature of the cell. The charging process should be stopped when the battery gets too hot. And the correct way to do it is by removing the batteries. 
  • In the fast charging phase, the NiMH battery charge most effectively. This way makes it easier to determine the charge’s point.
  • Evaluating the rapid charging capacity. Although NiMH batteries are charged at a fast phase, this is only sometimes the case. Understanding the datasheet is necessary.
  • Intermixing the chargers should be avoided. The reason is that each battery requires charge algorithms. 
  • There is a real threat of overcharging and the potential absence of a backup timed charging end. Manually inspecting the charge status will provide information if the battery is likely to be charged or terminated.

NiMH Cell Elements 

The cell of a NiMH battery consists of three main components:

Electrolyte

The electrolyte of this battery is a potassium hydroxide solution.  

  • Has the highest conductivity
  • Constant throughout the charge and discharge cycle
  • At charge range, a cell’s performance nearly remains constant.

Positive electrode

For the positive electrode, nickel hydroxide is its composition.

  • Proton exchanges take place in the charge-discharge reaction.
  • Enables mechanical stability at a high level 
  • Prolongs and improves lifecycle

Negative electrode

Active hydrogen is present in the negative electrode.

  • They are included in the cell as a metal hydride.
  • It has 2% stored weight.

NiMH Battery Characteristics 

NiMH batteries have excellent characteristics that allow them to stand out, with a few certain drawbacks. 

Effect on the environment 

NiMH batteries don’t contain toxic materials that could seriously affect the environment.

Output voltage 

A single cell from the battery can produce 1.2 voltages—the potential of making them a replacement could be possible.

Specific energy density 

NiMH cells have higher specific energy values between 60 and 100 W h / kg. That is the maximum energy a NiMH battery can hold within a volume of weight.

Self-discharge

Self-discharge is undeniably one of the downsides of NiMH batteries. The self-charge of this battery is relatively high at 3% per week storage. 

Charging 

This battery should be charged with extreme caution. NiMH is sensitive in terms of overcharging and other charge problems. 

Application 

Nickel-Metal Hydride power source is used for various electronic devices, like camcorders, transceivers, cell phones, and many other portable usages.

NiMH and Lithium-Ion Battery Differences

Aside from utilized material dissimilarities, Li-ion and NiMH batteries have numerous differences.

Consider the following.

Durability

The NiMH and Li-ion power storage are both durable. However, lithium batteries cannot withstand high-temperature states, specifically in sweltering weather. That means the NiMH has more lasting service and strength. 

Weight & Sizes

Lithium-ion batteries are lighter than NiMH due to their smaller sizes. However, NiMH cells have about 2200 mAH average – which has a higher capacity than 1500 mAh of lithium cells. 

Cost

In terms of manufacturing cost, NiMH batteries are more economical. With around 50% less compared to lithium batteries. 

Regarding battery development, Nickel-Metal hydride cells have about 75% lesser rates than lithium. 

However, NiMH batteries have other advancement procedure yet still has a lesser cost. 

Power

Both batteries can accommodate the same power capacity. However, lithium batteries quickly charge and discharge the power.

Design Properties

NiMH and Li-ions also have the following variations.

Property Differences NiMH  Li-ion
Energy Density 70 to 100 kWh/m3 80 to 200 kWh/m3
Efficiency 81% 99%
Power Density 1.5 to 4 MW/m3 0.4 to 2 MW/m3
Cell Voltage 1.2 V 3.6 V
Fixed Energy 1 to 80 Wh/kg 3 to 100 Wh/kg
Fixed Power less than 200 Wh/kg 100 to 1000 Wh/kg

Nickel-Metal Hydride Battery Advantages and Disadvantages

NiMH batteries provide multiple benefits to particular applications. However, they also have limitations. 

The following defines the NiMH’s pros and cons.

Advantages

Compatibility

NiMH cells have standard sizes, making them suitable for all your devices. They can handle about ten gadgets but not simultaneously. 

Safety

Nickel-Metal Hydride battery has fewer active materials. It stops when short circuits or overcharging occur. Moreover, this battery is safer than Li-ion, which possibly explodes if it gets overloads. 

Fully Dischargeable

NiMH batteries can be charged and discharged to 0% power. However, letting them reach reverse polarity can cause battery damage. 

Disadvantages

Extended Charging Period

The typical charging period of NiMH cells ranges from about 10 to 12 hours, more extended than lithium ones. Charging them in a speedy capacity will damage the battery. 

Increased Self-Discharge Rate

Each month NiMH cells drop a significant charge rate. About 5% weekly and 50% monthly. 

Unreliability

Since the NiMH cells rapidly self-discharging, they are not suitable for clocks. Instead, we recommend lithium or alkaline batteries. 

Tips To Prolong NiMH Battery Life

  • Cycle Charging- Fully discharging the battery and recharging it to 100% capacity is essential. You can perform such cycle charging until reaching the cells’ maximum level of operation.
  • Protect Against Reverse Polarity- Putting the battery into the wrong polarity is not recommended. Also, it is vital to prevent the cells from being in reversed polarity state. It may cause damage to a battery.  Using the E-devices auto shut-down feature is a great idea to control such conditions. When the battery has low power, it is advised to stop utilizing them. Instead, take out the cells from your device. 
  • Discharge Them When Not in Use- Discharging the power when not used will also help extend the battery’s life. It is essential to store the discharged unused batteries in cool and dry areas. 
  • Don’t Mix NiMH with Other Battery- Mixing lithium or alkaline batteries into NiMH can form harmful impacts on the cell. Mixing their battery packs is also prohibited. During the production process, the cells and packs are already paired. 

Following such tips can avoid cell damage and weak voltage output. 

How Long is the Lifespan of NiMH Battery?

Nickel-Metal Hydride batteries are rechargeable even multiple times. However, it has about five years of lifespan or less. The battery’s long life service makes them a cost-effective power solution for every suitable device. 

Conclusion

Knowing the benefits and shortcomings of nickel-metal hydride batteries will indeed help you decide if it’s the right cell for your projects.

You can always count on our services for further information and ordering assistance. Feel free to contact us!

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