Author Topic: Eneloop Self Discharge Study  (Read 7035 times)

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Offline SilverFox

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Eneloop Self Discharge Study
« on: March 25, 2007, 01:22:04 AM »
Sanyo started the ball rolling with low self discharge NiMh cells with the introduction of their Eneloop cells. I, along with several others, have been testing these cells for roughly a year now and they seem to be holding up to the manufacturers claims.

Sanyo claims 2000 mAh for their AA cells, and we are finding that to be very close. Sanyo claims that they can be used right off the shelf, and that also seems to be true. Sanyo also claims a cycle life of 1000 charge/discharge cycles. I would love to be in a position to check this out, but, for now at least, we will just have to believe them on this. The final claim is that they will still have 85% of their initial capacity after 1 year of room temperature storage.

This is what I found:

Here is the initial test data on these cells



You can see that they are very strong performers. I even included the data from the 30 day self discharge for comparison.

I then took a pair of cells and stored them on a shelf in my house. Data was taken at 0, 30, 90, and 180 days. Here is what that data looks like.



You can see that the biggest drop in capacity comes in the first 30 days. After that, things settle down. Looking at the numbers we have about 93% of the initial Amp Hours after 30 days and about 91% of the initial Watt Hours for the same time period. At 90 days we have about 88% of the initial Amp Hours and about 85% of the initial Watt Hours. At 180 days we have about 86% of the initial Amp Hours and about 82% of the initial Watt Hours.

I can easily see how these cells could still have 85% of their initial capacity at the end of a year. I am only going to project out to the year mark because I am going to be using my cells. Someone else can do the 1 year testing…

I did not note the voltage of the cells at 30 and 90 days, but at 180 days each cell was at 1.313 open circuit resting volts.

Several people have reported their self discharge test results and they seem to be quite low for normal NiMh cells. A lot of published information has NiMh cells in the 1-1% per day self discharge range. I was seeing around 0.7% per day with several brands of cells, based on short term tests of around 30 days. This seems to still be a little high for healthy cells. The problem 2500 mAh cells will completely self discharge in around 10 days so keep in mind that I do not consider those cells “healthy.”

Here is a graph of NiMh self discharge rates comparing original cell chemistry to the Eneloop cell chemistry.



The 0.7% per day line is pretty close to what I, and others, have reported, but it seems to be pessimistic at 90 days and beyond.

The question of the suitability of the Eneloop cells for use in a remote control or other low drain device has often come up. We know that the self discharge rate is faster early on, then it tapers off. I was concerned that there would be little difference between the normal chemistry rate and the Eneloop chemistry rate, initially, and there might be little advantage in using the Eneloop cells in applications like this. This study indicates that even at the 30 day self discharge rate, the Eneloop chemistry is a lot better.

Tom

Offline Geologist

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Re: Eneloop Self Discharge Study
« Reply #1 on: March 25, 2007, 11:01:26 AM »
Thanks for your post SilverFox - I will make this thread a sticky.

Are there other companies (or vendors) making the same or similar chemistry at a reduced cost?  My other thread regarding a possible conversion to Li-ION chemistry is - in part- due to the self-discharge of regular NiMH cells.
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Offline SilverFox

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Re: Eneloop Self Discharge Study
« Reply #2 on: March 25, 2007, 08:32:18 PM »
Hello Geologist,

There are a variety of low self discharge cells available.  I am just starting to check some of the others out.

The self discharge rate of NiMh cells only becomes an issue if you don't use your lights.  I would suggest that you use them more often... :)

A NiMh cell in good condition will loose about 50% of its capacity on roughly 100 days.  It is up to you to use the other 50%.

Tom

Offline Lips

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Re: Eneloop Self Discharge Study
« Reply #3 on: March 26, 2007, 01:33:41 AM »
Thanks for the graphs Tom   :thumbup:
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Offline Lightstream

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Re: Eneloop Self Discharge Study
« Reply #4 on: April 13, 2007, 04:54:59 PM »
Awesome.. now I can recommend them with test data to back me up :)
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Offline Aten_Imago

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Re: Eneloop Self Discharge Study
« Reply #5 on: August 07, 2007, 12:27:07 PM »
Thanks for the excellent and relevant data! A lot of us use R NiMH's in  many devices that are not used daily and having this knowledge is a big help. As you astutely point out the key is either to use or recharge at some point in the first month. Because I need the extra juice afforded by higher MAH batts for my digicam, I don't have much use for low discharge cells except in flashlights, radio and remotes.

Offline xeccon

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Re: Eneloop Self Discharge Study
« Reply #6 on: January 06, 2012, 07:13:33 AM »
GOOD review and relevent data about Eneloop battery :thumbup:

It is very forceful to demonstrate some function and characters of this branded battery.