Low self-discharge NiMH battery

Low self-discharge NiMH battery

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The low self-discharge nickel-metal hydride battery (LSD NiMH) was introduced in November 2005. These batteries were developed by Sanyo
is a major electronics company and member of the Fortune 500 whose headquarters is located in Moriguchi, Osaka prefecture, Japan. Sanyo targets the middle of the market and has over 230 Subsidiaries and Affiliates....

, who called them "eneloop
- Description :The eneloop rechargeable batteries were developed by Sanyo and introduced to the market in November 2005. They lose their charge slower than previous NiMH batteries: 10% in the first year compared to about 20% on the first day and 1-4% on every successive day. Hence the name, low...

". Subsequently, other manufacturers also offered LSD NiMH.

This kind of battery reduces self-discharge
Self-discharge is a phenomenon in batteries in which internal chemical reactions reduce the stored charge of the battery without any connection between the electrodes...

 and, therefore, lengthens shelf life compared to normal NiMH batteries. By using improved separator and improved positive electrode, manufacturers claim the batteries retain 70 to 85% of their capacity after one year when stored at 20 °C (68 °F), while standard NiMH batteries may lose half their charge in this time period. Retention of charge depends a lot on the battery's impedance or internal resistance (the lower the better), the size of the battery as well as the mAh rating. High quality separators are also very important. Thick separators take up space and reduce capacity, while providing a low-tech way of reducing self discharge. Thin separators tend to raise the self discharge rate. Some batteries may have overcome this obstacle with more precise manufacturing techniques and by using a more advanced sulfonated polyolefin separator.

When compared to regular NiMH batteries, low self-discharge types are most useful when there is more than three weeks between charge and discharge to empty on average, or to ensure stored devices are usable several weeks after charging of batteries. Specifications for the self discharge rate are not always clear or widely published, and virtually any LSD may claim to maintain some level of charge after 12 months. A non-low-self discharge battery typically self discharges at a rate of about 20% within the first 24 hours, then from 1% to 4% per day thereafter.

In devices not accurately calibrated to closely predict battery level, run-times for LSD NiMH batteries can be as good or even better than normal cells with higher rated capacity, because the slightly higher operating voltage doesn't trip a device's under-voltage shut off circuit.

Batteries with low internal resistance waste less energy and capacity on heat during rapid discharge and recharge. Low self-discharge NiMH batteries typically have significantly less internal resistance than traditional NiMH batteries.

There are many brand names for LSD NiMH batteries. Most manufacturers produce only size AAA and AA batteries, and most low self discharge batteries are sold in these sizes. C and D cells are available, though some are AAs inside a C/D-sized case. Several manufacturers also offer 9v (PP3) LSD NiMH batteries, rated between 150mAh and 250mAh.

Developments 2011

Varta (USA: Rayovac) and Ansmann increased their LSD NiMH batteries' capacity to roughly 2300 mAh.

Sanyo introduced new version of its Eneloop batteries with increased capacity and life expectancy. The eneloop plus incorporates a PTC thermistor that cuts the power when the battery overheats in order to make them safe for use in toys for small children.