How To Charge NiMH Batteries?


Batteries have a great advantage for industries producing electrical components and products. Consider a company like Tesla that has to manufacture electric vehicles every day. When it produces electric cars, it needs batteries, though high-quality ones. But this production of products also demands the right battery at its disposal. Only rechargeable batteries offer the solution. Rechargeable battery types include NiMH batteries. A NiMH battery is a rechargeable battery, also going by the name of nickel metal hydride battery. All rechargeable batteries have a basic phenomenon of operation, such as two electrodes within which the cells flow. In this read, we will be discussing the NiMH batteries in detail, highlighting all the aspects of NiMH rechargeable batteries.

What is a NiMH Battery?

A rechargeable battery charges itself through the help of flowing cells within the two electrodes in a battery. All batteries offer and perform the basic function of keeping a product working for longer. When you study a battery, you will see that its charging power to the product is significant. They are truly the real concept behind portable products. A portable product does not need a physical connection throughout its operation. You can charge these products and then use them at different places. Batteries such as NiMH rechargeable batteries are types of rechargeable batteries that happen to solve excessive charging problems.
In truth, the rechargeable concept is batteries such as NiMH batteries do not happen by a conscience. In essence, this happens through the movement of cells within two electrodes. Cells move between a positive electrode and a negative one, and they thus flow back. This to-and-fro movement causes the cells to ionize and energize. And in such a way, the batteries charge. In a NiMH battery, you will find the positive electrode made from nickel oxide hydroxide. The negative electrode consists of an allow that absorbs hydrogen.
We will be discussing the true details of these batteries in detail. However, in a summarized manner, you will know the true power and capacity of NiMH batteries rechargeable. These batteries will offer more capacity and strength to your products. A NiMH battery carries around three times more capacity than a nickel-cadmium battery. Increased capacity means more working and operating life. Thus, you can ease off the worry of charging your devices again and frequently to serve the purpose. When it comes to energy densities, this same rechargeable NiMH battery has a higher density than the nickel-cadmium one. However, this capacity is lower than lithium-ion batteries.

Working Principle of NiMH Batteries

Nimh batteries, like all rechargeable batteries, have great strength, capacities, and operating life. But when it comes to their working principles, the basics do not change either. Within this and other rechargeable NiMH batteries, you will find two electrodes, positive and negative. The cells move within these electrodes, get charged through their movement, and ensure the battery remains recharged for longer operations. But this is not everything that is about a NiMH battery that you must know. These batteries operate on the true physical principle of charging and discharging.
Nimh batteries consist of two electrodes, positive and negative, which we call cathodes and anodes. Apart from this, these batteries consist of two distinct elements at these electrodes. The positive electrode contains nickel oxide hydroxide, whereas the negative electrode consists of a hydrogen-absorbing alloy. Like all rechargeable batteries, the electrodes are separated by a permeable membrane. Within this separation, the electrons and ions flow from the positive electrode to the negative one and vice versa. This movement energizes them and causes the aa NiMH rechargeable batteries to power up, just like the aaa NiMH rechargeable batteries.
Talking a bit about the structure, the battery consists of two electrodes at either end with a permeable membrane at the center. This membrane is immersed in a solution of potassium hydroxide (aqueous). When the entire recharging procedure happens, there is no significant change in the battery operating life or the operation itself.

NiMH Battery Charging

A battery needs to be charged, and it is the basic principle of any charging device. Rechargeable NiMH batteries have to be charged to perfection to avoid any mishap. We stress this factor for this special battery type since it is prone to damage even with a sudden mishap or error. Moreover, when it comes to their formulation, they are not stronger to absorb changes in their charging. Thus, charging NiMH batteries needs to be brought into full care. A general concept of charging NiMH batteries is that they need not be overcharged in any manner.
Charging the NiMH cells in a NiMH battery pack is a difficult task in comparison to counterparts such as nickel-cadmium cells. It is because the peak and fall of the voltage to detect a full charge are smaller in the NiMH batteries. When you overcharge the NiMH batteries, you cause them to overheat, and thus there happens damage within the cells. As a result, it causes a loss in capacity, and there is no other battery apart from the NiMH battery that is highly prone to this. So it leads to a big confusion about how to accurately, timely, and effectively charge these batteries for a better result. For this, we will be presenting some methods of charging.

How to Charge NiMH Batteries?

To charge a NiMH battery, you can develop and follow any of the below methods. However, it is essential to know that for charging these batteries efficiently, you will need a good NiMH battery charger. At this time, it is the method you need to charge them. There are altogether four methods that we will be presenting to you for ideally charging your batteries. But do not forget the golden rule regarding charging these batteries, that you must not overcharge these batteries at all.

1. Time Charging

The simplest method of charging a device is to keep a record of the charging time. It is because, with time, you almost nullify the possibility of errors such as overcharging. But when the timekeeping device shows an abnormality, there is a straight effect on your battery. In addition to this, this same error is the only negative thing about following the timekeeping prospect of charging NiMH batteries. Implementing it is another additional task. It is because regular chargers do not come equipped with a timer. For this, you must infuse or install them within the chargers. This entire process gives you an indication of the actual time your device needs to charge.

2. Thermal Detection

Thermal detection, or simply sensing the full charge by observing the temperature rise, is another method to check and charge NiMH batteries. In such a method, the focus is on sensing the temperature during the end of the charge, thus identifying fully charged time through the rise of temperature. The simplest way is to check for the hotness of the cells that a temperature detector can display. But limitations do come with such a method; for example, you cannot predict if the hotness is showing a full charge. It can be that a cell is hot from the center but even hotter from the inside. Thus, the detection will go wrong, and the entire process will be faulty.

3. Negative Delta Voltage Detection

A drop in the voltage can also indicate the charging capacity, which is a full charge. This happens as a slight drop in the voltage is observed once the NiMH batteries are fully charged. The same method of charge detection was used in nickel-cadmium batteries. However, this is no longer widely found. The problem with utilizing such a method with rechargeable NiMH batteries is that they show a minimal voltage drop. Thus, when designing a charger, you must make it able to detect a voltage drop of around 5mV per cell. But for such efficiency, you will need to remove the sound effects.

4. Fast Charging NiMH Batteries

Charging your 7.2 v NiMH battery or the 8.4 v NiMH battery never eases the concept of charging. When you slowly charge these batteries, you will not be able to detect either the 5mV voltage drop or the temperature rise. And once you fail to detect the endpoint, you will not be able to keep your NiMH batteries away from damage. For this, try to avoid the slow charging NiMH battery methods and insist on using faster methods.


NiMH batteries are a great exponent for keeping the devices working for longer. With good speed, capacity, and power, they often become helpful alongside one to take care of. For example, their charging methods may appear simple, but they require extreme care from your end. For this, you must involve new methods and ways to charge them, avoid damages and malfunctions, and thus keep the working fluid. Most people like to ask how long NiMH batteries last. Being rechargeable batteries, you can easily recharge them hundreds of times, and they work superbly for around five years. This also means that they can operate equivalent to hundreds of alkaline batteries during their combined lifespan.

Leave a Reply