9

In the following pages:

it is mentioned that the Eneloop battery has

has an even lower self-discharge

[…]

in comparison with other high quality rechargeable batteries, eneloop retains 70%*1 of its charge after 5 years of storage and does not require periodic recharging.

[…]

you can count on eneloop supplying the power that you need, even three years later.

[…]

The durability of SANYO’s original super-lattice alloy, a negative-electrode material used in eneloop, has been enhanced by homogenizing the crystalline structure (a reduction of crystals with an irregular atomic order is irregular) as well as improving its composition (the ratio of constituent element) to reduce the deterioration of the super-lattice alloy by repeated charge and discharge

Does it work?

  • 1
    I can't link to a study, but I am a huge fan of Eneloop batteries. They absolutely have longer charged shelf-lives than any other rechargeable I've used. – Larry OBrien Oct 11 '12 at 20:05
  • I have found eneloop batteries to be comically short-lived compared to other rechargeables, so I'm looking forward to seeing answers. – neilfein Oct 26 '12 at 2:20
  • Never used Eneloop, but I do use the Duracell Precharged rechargeable batteries and I'm very impressed with them. I left them on the shelf for months and they still had a decent amount of charge left in them. They don't hold a charge (and don't claim to) as the claims of Eneloop, but I find they hold quite a lot of charge as well. @neilfein states that Eneloop batteries don't seem to hold much of a charge. – Kibbee Oct 27 '12 at 17:51
  • I don't know of any studies comparing Eneloops to other batteries, but I have used them for a couple of years, and I can say they work as advertised. I use them for everything. Some of them sit unused for 6 months or more and still work as if freshly charged. I have not yet had a single one fail, out of about 20 I have in use. I don't use them in high-power devices though. – hdhondt Oct 28 '12 at 22:35
9
+50

Yes, low self-discharge (LSD) NiMH batteries function as described. By the way, the Eneloop brand, by Sanyo, is not the only LSD battery on the market. Other LSD NiMH batteries are sometimes marketed as "hybrid," or "pre-charged" NiMH batteries. Duracell "StayCharged" and Panasonic EVOLTA batteries are other good alternatives.

Here's the basic method of why these batteries self-discharge at such a lower rate than traditional NiMH cells:

Every battery cell has an anode and a cathode. Most batteries are just several cells placed together in a series (to increase voltage), or in parallel (to increase capacity). It is common to see a combination of series and parallel to achieve specific voltages and reserve capacity.

In order to keep the cells from shorting themselves out, a separator has to be placed between the anode and cathode (negative and positive electrodes, respectively) that also allows the transport of ionic charge carriers, which are needed to complete the circuit during the passage of current.

The more efficient this separator is at isolating and separating the cathode and anode from each other, the longer it will take to self-discharge the cell.

A separator generally consists of a polymeric membrane forming a micro-porous layer. It must be chemically and electro-chemically stable towards the electrolyte and electrode materials, while remaining durable enough to withstand the high tension of battery construction. Their structure and properties considerably affect the battery performance, including the batteries energy and power densities, cycle life, and safety.

Having a thinner separator inside the cell provides the space necessary to increase its capacity, which leads to longer shelf life (requiring more time to discharge at the same rate) as well as longer application use.

The more efficient the separator is at trapping shuttle substances, the slower the battery will self-discharge. This is all evident in a study done some time ago:

The suppression mechanism of the self-discharge reaction in nickel-metal hydride batteries using a sulfonated polyolefin separator was investigated with sealed-type AA size cells. The experimental results indicate that a sulfonated polyolefin separator effectively suppresses the self-discharge reaction in nickel-metal hydride batteries by trapping nitrogen-containing redox shuttle substances. It is also found that a sulfonated polyolefin separator traps the shuttle substances as gaseous ammonia. In the experiment examining the influence of the amount of the shuttle substances on the self-discharge, the starting point of the self-discharge agreed well with the point at which the nitrogen adsorption capacity of a sulfonated polyolefin separator reached its maximum.

Suppression mechanism of the self-discharge reaction in nickel-metal hydride batteries using a sulfonated polyolefin separator, from the Research on Chemical Intermediates journal, Volume 32, Number 5 (2006), 453-459.

I hope this answers your question.

TL;DR: Yes, they last longer/self-discharge slower.

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