nimh battery overheating

NiMH Battery Overheating: 4 Causes & Solutions

NiMH batteries are often used instead of LiPo batteries in RC devices. They are cheaper than the LiPo batteries with excellent reliability. But some issues can affect the battery performance. 

Overheating of the NiMH battery is such an issue. No one wants their battery to get too hot.

But why is the NiMH battery overheating?

Several reasons can cause the NiMH battery to overheat. Fast charging the battery is one of the reasons. Also, the NiMH battery can get hot due to overcharging.  Internal problems can raise the temperature too. A battery can also get hot when it has internal damage. Lastly, overuse can cause heat too.

This is only the starting. There are more insights into the overheating issue. I have discussed the problems and solutions right here. So please come with me to solve this problem!

Is the NiMH Battery Overheating? 

Just like the overheating of LiPo batteries, NiMH batteries getting hot is very common. But not every incident of rechargeable batteries getting hot is serious. So at first, it’s important to ensure that the battery is getting hot above the safety point. 

Chemical reactions take place within the battery while charging and discharging. These reactions are exothermic, which means they produce heat as a byproduct. 

So the temperature of the battery rises. This rise can not be stopped.

NiMH Battery
Source: ubuy.com.bd

But there is a limit to the temperature enhancement. If this limit is crossed, only then the heating can be termed overheating. 

The charging temperature of a NiMH battery can go as high as 120-130° Fahrenheit. It is an issue for the battery if it gets hotter than this.

So don’t get worried if the NiMH or lithium-ion battery gets hot when charging. But why does the incident of battery overheating happen? Well, to know that you will have to scroll below. I have discussed the causes behind this problem there.

Causes Behind NiMH Battery Overheating 

Before solving any problem we must know the reasons behind the problem. So we must mark the reasons behind NiMH battery overheating. I have tried to cover the problems in detail here. Have a look at it. 

Fast Charging 

This is a very common reason behind the NiMH battery getting hot. Fast charging is the process of fully charging the battery within a short time. In this process, the battery chargers work at a very high electrical potential. 

In this way the rate of charging increases. The chemical reactions also become fast and occur multiple times. As a result, the temperature of the battery gets high. 

The experts do not encourage the frequent fast charging of NiMH batteries

Damaged Battery

Sometimes the NiMH battery can get hot due to internal problems too. There are many factors of the RC battery that determines its functionality. 

Batteries last for a certain period. Then they get damaged. 

There are several symptoms of a damaged battery. Getting hot easily is one of them. So you must check the battery if it gets hot easily. It can be a potential threat to you and your RC device.

Overcharging 

Another reason behind the high temperature of NiMH batteries is overcharging. Overcharging means charging the battery even after its capacity is full. 

Doing this is very harmful. This phenomenon also decreases the lifespan of NiMH batteries.

Now, what happens when a NiMH battery is overcharged?

When a NiMH battery is overcharged, some adverse chemical reactions take place within it. The oxygen recombines with the positive terminal of the battery. Here a small fire takes place, and this incident is called oxidation. Thus the battery gets heated. 

Too Much Load on the Battery 

Using the NiMH battery for a long period can also increase its temperature. Batteries are pretty sensitive objects. 

They are very small with strong chemical reactions taking place within them. Overuse can easily make them hot.

Often we use the RC car or drone for an extended time. The battery is drained to zero and then it is charged again. 

Doing this creates pressure on the battery. The battery can get damaged and very hot due to long usage and continuous draining.

NiMH battery is overcharged
Source: rcgeeks.co.uk

These are the main reasons that cause the overheating of NiMH batteries. These reasons are responsible for AA battery overheating & lithium battery overheating too. 

In the next section, I will show you the ways to overcome these issues.

Solutions to NiMH Battery Overheating 

The solution to overheating NiMH batteries is not as complex as solving RC rear wheel problems. You have to take some easy measures to ensure the safe temperature of the batteries. Let’s see them in detail below. 

Charge at Ideal Rate 

Though fast charging is very tempting, it is better to charge at the ideal rate. 

Yes, I know that fast charging saves a lot of time. But it is not always safe for the battery. If charged at the ideal rate, the longevity of the NiMH batteries increases. 

The manufacturers also suggest maintaining the ideal rate. Even the warranty of the battery can get void if fast chargers are used. So use the manufacturer suggested chargers to charge the battery at the suggested voltage.

Do Not Overcharge the Battery 

Unplug the charger as soon as the battery is fully charged. This is beneficial for both the battery and the charger. 

The lifespan of both these devices extends by following this one simple rule. Different problems with the battery are also avoided in this way. 

You can also use smart chargers to accomplish this task. Many modern chargers can detect if the battery is fully charged. Then the charging stops automatically.

Charge at Ideal Rate
Source: bigsquidrc.com

Though these chargers cost more, they are worth the money. When it comes to smart chargers for your RC I have a few favourites. Some of my go-to digital chargers for RC are listed below: 

LiPo Charger Lipo Battery – Has multiple functions and universal voltage capability. 

Tenergy TB6-B Balance Charger Discharger – Works with most voltages, has an easy-to-read screen and has wider connector capability. 

You won’t regret getting a smart charger. It makes the hassle of charging RCs much easier. 

Keep The Charger Cover Open

It is a simple hack that you can follow while charging the NiMH battery. Many chargers come with an enclosed system. The battery gets obstructed from all sides while charging. This can increase the temperature. 

So open the cover while charging the battery. This might not look cool, but it will certainly help to cool down the battery. 

Give Time to Cool Down 

A rise in temperature right after charging is normal. Do not use the charger as soon as it is done charging. Give it some time to settle down. 

Once the charger reaches the room’s temperature, connect it with your RC car or drone.

Replace The Damaged Battery 

If the NiMH battery is permanently damaged, you can’t stop it from overheating. There is no other way but to replace the battery in such instances. 

For replacing the NiMH battery you can look into the 7.2V 5000mAh NIMH Battery for RC Cars or the Zeee 8.4V 3000mAh NiMH Battery. Both of these batteries are godsent for RCs. 

It is very risky to use a damaged battery. Besides overheating, this type of battery also gets swelled. 

The battery can burst while charging or discharging if it is not fit. So replace it as soon as you see these symptoms. Or else the RC device can get damaged alongside the NiMH battery during discharging of the battery.

Use A Charger with Temperature Sensor 

This is another great way to extend the battery life by decreasing its temperature. 

Many Fast chargers nowadays come with temperature sensors. They can sense if the battery is getting too hot while charging.

If something like that happens, the fast charging mechanism turns off. The charging starts again when the battery is cool. In this way, you can get the benefit of a fast charger as well as a cool battery.

These are the methods of fixing the high temperature of the NiMH battery. These methods are also applicable for Duracell battery overheating & lithium-ion battery gets hot when charging. Follow these methods for the betterment of your battery.

Frequently Asked Questions (FAQs)

Can NiMH batteries explode? 

Yes, NiMH batteries can explode. But it is a very rare incident. Leakage of the battery generally causes the explosion. NiMH batteries are very protected from leakage. They rarely leak. So the probability of an explosion is also low. Yet it can still explode as it is a rechargeable battery.

Can NiMH catch fire?

Yes, NiMH batteries can catch fire. When the voltage of the battery gets too high, it can cause a fire. Also damaged NiMH batteries are prone to burning. Anyway, NiMH batteries don’t have too many flammable substances. Only the heat shrink tubing can catch fire. So the chances are pretty low. 

How long do NiMH batteries last?

NiMH batteries usually last for about five years. But this time is not fixed. It depends on lots of factors. The usage frequency plays an important role in the lifetime. Also, safe charging increases the battery lifespan. Under proper maintenance, the battery can last up to hundreds of cycles.

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