Eneloop Seeking ReviewsSome new facts about LSD cells you should know...
[Updated Oct 24, 2008]
My original review on the Sanyo eneloop NiMH cells was written nearly two years ago. Since then, I have learned a lot more about the characteristics about eneloop and other low-self-discharge cells. So it is time to clear up some inaccurate information I wrote about eneloop's self-discharge rate.
1. I was told that the Sanyo eneloop cells were not 100% fully charged when they leave factory. This makes sense because new cells are fast-charged in the factory to save time. In order to avoid problem with heat and gas built-up, they cannot be charged to 100%. I have tested some eneloop cells that were manufactured 20 months ago, and they still maintained about 70% charge. On the other hand, cells manufactured 6 months ago contain about 75% charge. This confirmed that the discharge rate is much lower than I previously estimated.
2. The self-discharge rate of eneloop (and other LSD cells) is not linear! My own testing showed that a fully charged eneloop may lose 10% of its initial charge during the first month of storage, but in the second months it may lose just 2-3%. The rate becomes even slower after three months. In fact, my 5-month self-discharge test using various brands of LSD cells gave nearly identical results as my previous 3-month test.
3. When an eneloop cell is freshly charged, its capacity actually measures at about 5% higher than its rated capacity (2100mAh vs. 2000mAh). In my previous tests, I used measured capacity as base to calculate the percentage loss. This results in apparently higher percentage loss. Had I used the rated capacity as base value, the self-discharge rate would be about 5% lower.
Based on the above revelation, I believe Sanyo's claim about eneloop (maintain 85% charge after one year, 80% after two year) to be accurate. Therefore the title of my previous review ("The News of LSD Has Been Slightly Exaggerated") has to be replaced.
Over the past two years, I have tested several different brands of LSD cells available from Amazon.com, including Rayovac Hybrid, Kodak Pre-Charged, and Duracell Pre Charged. They have all performed very well - practically no difference from the Sanyo eneloop. So the bottom line is: just pick which ever brand of LSD cell is on sale, and you can't go wrong.
LSD is great.... just keep away from heat!
According to Sanyo, the new eneloop LSD (low self-discharge) NiMH batteries can maintain 85% of its original charge after 1 year of storage. This claim is slightly misleading, because it is based on simulation test at 20 degree C. At higher temperature, the self-discharge rate is likely to be much higher.
I have tested five of those AA cells (details are given in my review for the eneloop 4-pack). The average energy loss is about 26% after less than 6 months of storage, based on manufacturer date codes. This self-discharge rate is about 3 times higher than what Sanyo claimed. However, it is still 6 times lower than that of ordinary NiMH batteries. Therefore I'm in the process of replacing most of my existing rechargeable cells to the Sanyo eneloop.
Thanks to lower self-discharge rate, you'll discover a lot more applications for eneloop cells in your house, such as in clocks and remote controls. Do NOT use those cell in smoke detectors, since their discharge voltage profile is very different from that of alkaline cells. Also, don't use them as emergency flash lights batteries in your car, because the higher temperature during summer time will probably nullify the advantage of LSD.
[Update on Jan 13, 2007]
I have tested six new eneloop AAA cells, dated "2006-06'. The average residue charge is 589mAh, and the freshly charged capacity is 827mAh. This implies a self-discharge rate of 29% in 7 months, which is consistent with the rate for AA cells (26% loss in 6 months).
[Update on Jan 29, 2007]
The Rayovac "Hybrid" rechargeable NiMH batteries are now available at Walmart, priced at only $[...] for 4-pack of AA or AAA cells. It is also advertised to have low self-discharge rate, but not as low as that for eneloop. The eneloop is supposed to retain 85% charge in 12 months (when stored at 20 degree C), whereas Hybrid is supposed to retain 80% charge in 6 months (no mention of temperature).
[Update on June 3, 2007]
In my 2-month self-discharge test using four different brands of NiMH cells. Hybrid and eneloop came up neck-and-neck!
Room temperature: 60-62 degree F (16-17 degree C). All capacities measured are average of 2-cells.
- Sanyo eneloop 2000, purchased Jan 2007.
Initial capacity measured: 2070mAh
Capacity after 62 days: 1796mAh (-13.2%)
(Note: my previous result for eneloop showed -18%, but I repeated the test and it did better this time)
- Rayovac Hybrid 2100, purchased Jan 2007.
Initial capacity measured: 2155mAh
Capacity after 62 days: 1859mAh (-13.8%)
- LaCrosse 2000, purchased Jan 2006.
Initial capacity measured: 1902mAh
Capacity after 62 days: 1417mAh (-26%)
- SONY 2300, purchased Sep 2004.
Initial capacity measured: 2210mAh
Capacity after 62 days: 1309mAh (-41%)
So neither eneloop nor Hybrid did as well as advertised, but they are still significantly better than previous generation of NiMH cells. So you can't go wrong with either brand.
After all It is not only about milliampere hours
I received several sets of Eneloops in February and label told they were produced in April - so they sat at warehouse for nine month. I put them into camera and they worked just fine. Kudos Sanyo!
I should also mention that Sanyo includes reusable battery holders with each set of four. These holders do not look very sturdy, but they perfectly usable.
Technically, Sanyo solved the main problem with NiMh technology - frightening self-discharge rate (up to 40% a month for standard cells). By doing this Sanyo reduced cell capacity down to 2000 mAh from today's top line of 2700 mAh.
Simple calculation shows that due to self-discharge a good 2700 mAh battery holds only around 2000 mAh after a month and a half.
So the answer to the question "which battery is better - Eneloop or standard NiMh" - lies in the usage pattern.
If you always keep batteries in your camera in top-notch charged condition, then standard 2700 mAh set is a winner. For occasional shooters who always forget to charge batteries (like me), Eneloop makes lot of sense because in three month I get around 1900 mAh out of Eneloop and only 1400 mAh from the standard cell. So Eneloop is a winner for everyone who keep batteries inside the camera or any other device for more than 6 weeks.
And, well, if paragraph above looks too technical with too many details and numbers - then Eneloop is a clear winner too, because it just behaves the way battery should behave - without forcing users to know how it works.
This observation made me buy additional sets of AAA Eneloops to use in my wireless mouse, keyboard, voice recorder and LCD flashlight. It should be taken into account that Eneloops are four times more expensive than Alkaline cells, so it is reasonable to use them for devices that require fresh batteries at least twice a year.