New generation Ni-MH rechargeable batteries

Alkaline batteries, thanks to their readiness for immediate use after purchase and thanks to their energy retention for a relatively long period of time, were a better alternative to traditional rechargeable batteries in the past. What has changed after the introduction of the new generation of rechargeable batteries?

There has been no major revolution in the field of powering small electronics for a long time. There were both reinforced alkaline batteries, low-efficiency zinc-carbon batteries and nickel-metal hydride Ni-MH batteries on the market. But the latter remained somewhat in the shadow of single-use cells - they were characterized by poor durability, few charge/discharge cycles, did not maintain capacity during longer storage - they required charging immediately before planned use, and cheap chargers, due to the simplicity of their design, were not able to charge them optimally. These factors, along with the high price and lack of readiness for use immediately after purchase, have overshadowed the advantages of traditional nickel-metal hydride cells. It didn't help that Ni-MH batteries are much more efficient in devices with medium and high power consumption, and in addition, unlike batteries, they maintain hermetic tightness throughout their life - they do not spill out.

The situation changed dramatically after Sanyo launched the world's first new generation of Eneloop rechargeable batteries in typical sizes AA (R6) and AAA (R03) in 2005. Currently, the Eneloop brand belongs to Panasonic. These cells were characterized by a very low level of self-discharge, thanks to which charged batteries could retain a lot of energy even after several years after charging. Eneloop cells also owe their success to their high initial charge level using solar energy. The Japanese manufacturer was the first to be able to provide 70-75% battery charge already during the production process.

This feature has made the cells ready for use immediately after purchase, and the very high durability means that they are able to replace up to 2100 alkaline batteries, which is undoubtedly economically beneficial and contributes to care for the environment.

Rechargeable batteries from reputable companies usually have two series of products: standard – designed for typical and undemanding applications – and professional, designed for use in professional devices, e.g. in photographic equipment. They most often differ in capacity, expressed in milliampere-hours (mAh) – the higher the capacity of the battery, the longer it should work in the device. In the case of Eneloop rechargeable batteries, there are two types: Eneloop (white) and Eneloop Pro (black). The white version of these cells it has a minimum capacity of 1900 mAh in the R6 AA size and 750 mAh in the R03 AAA size. The eneloop Pro has a minimum capacity of 2500 mAh for the R6 AA size and 930 mAh for the R03 AAA size. The professional version, in addition to higher capacity, also has the ability to give off a higher current, which is important, for example, in camera flashes. The higher capacity and the ability to load with high current in the Pro version have reduced the durability of these cells, which in this case is about 500 charging cycles.

After the successful introduction of new generation rechargeable batteries with low self-discharge by Sanyo, other leading battery manufacturers, including Energizer, Duracell, Varta, GP, Fujitsu - have also introduced new generation batteries with low self-discharge to their offer. However, they were not able to jeopardise the market position of Eneloop batteries or match their quality in terms of the number of charging cycles or the level of self-discharge over time. Also, their charge level in the production process was often too low, which made it impossible to use them immediately after purchase.

The new generation of cells can be used as replacements for ordinary batteries (ready to use right away) in most devices (e.g. remote controls, alarm clocks, portable radios, mp3/mp4 players, flashlights, etc.). Examples of the latest generation of cells are Panasonic Eneloop, GP Recyko, Panasonic Evolta (formerly Infinium) and Varta Ready2Use, Fujitsu, everActive.

Next-generation Ni-MH battery technology

Modern Ni-MH batteries consist of two electrodes (anode and cathode), separated from each other by a porous plastic separator. All the components of the cell are rolled and placed in a metal container, and then filled with electrolyte. The metal container is closed tightly with a lid.

Self-discharge of Ni-MH batteries occurs for 3 reasons:

• chemical dissolution of the cathode
• natural decay of the anode
• anode contamination

How is self-discharge reduced? - using eneloop cells as an example

The chemical dissolution of the cathode was reduced by the use of a special alloy characterized by a crystal lattice structure (Superlattice Alloy). The use of this alloy also allowed to increase the capacity of the battery and reduce internal resistance, which in turn allows the use of a higher discharge current.
An additional advantage of using this alloy is that less cobalt can be used to stabilize the entire process than in cells produced using the old method.
The anode is protected with a special metal that slows down its natural decay. The electrolyte and separator have also been improved.

What are the important aspects of using and maintaining new generation batteries?

These cells do not require special treatment or forming. Nevertheless, due to the differences in the factory charge, it is recommended to initially fully charge them in a suitable charger – this will ensure optimal operation in the target device, and may also prevent over-discharge of new batteries. Eneloop rechargeable batteries can be a certain exception to this rule – we usually get them evenly charged and ready for immediate use. The new generation of rechargeable batteries also do not have a "memory effect", so they use their entire capacity. However, it is worth remembering that they will achieve the best parameters when they are charged using an advanced processor charger.

What to watch out for when using rechargeable batteries?

For rechargeable batteries during everyday use, the most harmful is permanent, complete discharge. Therefore, it is particularly important to use only the same batteries from the same manufacturer, with the same degree of charge in your device. Frequent complete discharge is harmful to the battery, so it is better to recharge it before planned strenuous use. When not in use, batteries should be stored at least partially charged, preferably in a cool place, in a dedicated protective container.

Are all batteries available on the market new generation cells?

Batteries made in older technology are still available on the market. In their case, remember to charge them before use. They can also lose charge level in a very large amount of fast pace – up to 30% after the first day of charging. In addition, when choosing batteries, it is worth paying attention to their brand / manufacturer. The least risk is associated with selection of proven batteries with real parameters. Remember that for the AA/R6 battery, the highest technologically possible capacity is about 2600 mAh, while for the R03 AAA it is about 1000 mAh. There are a lot of poor quality batteries on the market with significantly inflated parameters (even by 1000%) - the purchase of such cells usually brings a lot of disappointment and can effectively discourage the use of any reusable batteries.

A good battery is only part of the success – choosing the right charger is just as important.

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