Next-generation Ni-MH rechargeable batteries

Alkaline batteries, due to their readiness for immediate use after purchase and their ability to retain energy for a relatively long period, were previously a better alternative than traditional rechargeable batteries. What has changed with the introduction of new generation rechargeable batteries?


In the field of powering small electronics, there has not been a major revolution for a long time. The market had both enhanced alkaline batteries, low-performance zinc-carbon batteries, and nickel-metal hydride (Ni-MH) rechargeable batteries. However, the latter remained somewhat overshadowed by single-use cells - they were characterized by poor durability, a small number of charge/discharge cycles, did not maintain capacity during long-term storage - they required charging immediately before planned use, and cheap chargers, due to their simple design, were unable to optimally charge them. These factors, along with high prices and lack of readiness for use immediately after purchase, overshadowed the advantages of traditional nickel-metal hydride cells. It did not help that Ni-MH batteries are definitely more efficient in devices with medium and high energy consumption, and additionally, unlike batteries, they maintain hermetic tightness throughout their entire lifespan - they do not leak.

The situation changed dramatically with the introduction to the market in 2005 by Sanyo of the world's first next-generation rechargeable batteries under the Eneloop brand in standard AA (R6) and AAA (R03) sizes. Currently, the Eneloop brand belongs to Panasonic. These cells were characterized by a very low self-discharge rate, allowing charged batteries to retain a lot of energy even after several years of being charged. Eneloop cells also owe their success to a high initial charge level using solar energy. The Japanese manufacturer was the first to ensure that batteries were charged to 70-75% during the production process.

This feature meant that the cells were ready for use immediately after purchase, and their very high durability allows them to replace even 2100 alkaline batteries, which is undoubtedly economically beneficial and contributes to environmental protection.

Rechargeable batteries from reputable companies usually have two product lines: standard - intended for typical and non-demanding 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 operate in a given device. In the case of Eneloop batteries, we have two types: Eneloop (white) and Eneloop Pro (black). The white version of these cells has a minimum capacity of 1900 mAh in size R6 AA and 750 mAh in size R03 AAA. Eneloop Pro has a minimum capacity of 2500 mAh for size R6 AA and 930 mAh for size R03 AAA. The professional version, in addition to higher capacity, also has the ability to deliver higher current, which is important, for example, in flash units for cameras. The higher capacity and ability to handle high current of the Pro version reduced the durability of these cells, which in this case is about 500 charge cycles.

After the successful introduction of next-generation rechargeable batteries with low self-discharge by Sanyo, other leading battery manufacturers, including Energizer, Duracell, Varta, GP, Fujitsu - also introduced next-generation rechargeable batteries with low self-discharge into their offerings. However, they were unable to threaten the market position of Eneloop batteries or match their quality in terms of the number of charge cycles or self-discharge rate over time. Their charge level during the production process was often too low, which prevented their use immediately after purchase.

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

Next-Generation Ni-MH Rechargeable Battery Technology

Modern Ni-MH batteries consist of two electrodes (anode and cathode), separated by a porous plastic separator. All elements of the cell are rolled and placed in a metal container, which is then filled with electrolyte. The metal container is sealed tightly with a cap.

The self-discharge of Ni-MH batteries occurs for 3 reasons:

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

How was self-discharge reduced? - using the example of eneloop brand cells

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

What are the important aspects of using and maintaining next-generation rechargeable batteries?

These cells do not require special treatment or conditioning. Nevertheless, due to the differences in factory charge, it is recommended to initially charge them fully in an appropriate charger - this will ensure optimal operation in the target device and may also prevent excessive discharge of new batteries. A certain exception to this rule may be Eneloop batteries - they are usually received evenly charged and are ready to use immediately. Next-generation rechargeable batteries also do not have a "memory effect," allowing them to utilize their full capacity. However, it is worth remembering that they will achieve the best parameters when charged using an advanced smart charger.

What should you particularly watch out for when using rechargeable batteries?

For rechargeable batteries, the most harmful during daily use is permanent, complete discharge. Therefore, it is particularly important to use only the same batteries from the same manufacturer with the same charge level in the device you own. Frequent complete discharge is harmful to the battery, so it is better to recharge it before planned intensive use. Unused 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 next-generation cells?

Batteries made with older technology are still available on the market. In their case, it is important to remember to charge them before use. They can also lose their charge level at a very fast rate - even 30% after the first day of charging. Additionally, when choosing batteries, it is worth paying attention to their brand/manufacturer. The least risk is associated with choosing proven batteries with real parameters. Remember that for an AA/R6 battery, the highest technologically achievable capacity is about 2600 mAh, while for R03 AAA it is about 1000 mAh. There are many low-quality batteries on the market with significantly inflated parameters (even by 1000%) - purchasing such cells usually leads to significant disappointment and can effectively discourage the use of any rechargeable batteries.

A good battery is only part of the success - choosing the right charger is equally important.

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