Li-Ion Self Discharge Rate Test

SilverFox

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On March 24, 2005 I charged an unprotected 18650 Li-Ion cell up to 4.000 volts and placed it in room temperature storage. A few hours later it was at 3.989 volts.

On March 26, 2005 it was at 3.976 volts.

On May 14, 2005 it was at 3.975 volts.

On October 1, 2005 it was at 3.974 volts.

On December 11, 2005 it was at 3.973 volts.

On February 10, 2006 it was at 3.973 volts.

On March 2, 2006 it was at 3.973 volts.

On April 19, 2006 it is at 3.973 volts.

Not much in the way of self discharge...

EDIT: I tested this cell for remaining capacity, then charged it back up to 4.000 volts and checked the capacity again. After 1 year of room temperature storage, this cell had 95% of its original capacity. END EDIT

Tom
 
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MrAl

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Hi again Tom,

Didnt we establish at one time that the charge is not related to the
open circuit voltage? On the other hand, it's also hard to believe
that the charge could change that much and not even show one
millivolt of change in the open circuit voltage. I dont know for
sure though because i have no graphs in front of me.

Take care,
Al
 

SilverFox

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Hello Al,

Li-Ion is similar to lead acid in that you can get an approximation of the state of charge by measuring the resting open circuit voltage.

Tom
 

WAVE_PARTICLE

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that sounds great, but how does this compare to other rechargeable chemistries like NiMH and NiCd?

Thanks for the data!! :thumbsup:

WP
 

LEDcandle

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There have been a couple of threads on NiMh discharge rates; it is approx 2% a day. I don't know where they bottom out (0.8v - 1v?) though and whether they discharge all the way to that bottom.

My Li-ons don't discharge much either; I was mentioning in another thread, for those folks that let their fresh-from-charger Li-ons sit for a few days in hopes that they will drop from 4.2v to 3.7v so that they can use their Li-ons in a 7v light, pls note Silverfox's findings as that doesn't happen :D
 

WAVE_PARTICLE

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Wow....what a difference!

Assuming that the laws of thermodynamics are obeyed, am I correct to assume that the lost energy is in the form of heat generated by the battery? Just wondering, that's all....

WP


LEDcandle said:
There have been a couple of threads on NiMh discharge rates; it is approx 2% a day. I don't know where they bottom out (0.8v - 1v?) though and whether they discharge all the way to that bottom.
 

changsn

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I thought there was a concern that although the voltage is essentially the same, that the capacity of the battery may have diminished considerably. When were you planning on doing a discharge?

Sam
 

changsn

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Tom - I thought Li Ions do not like to be at full charge and their longevity is affected hence the store at half charge recommendation. So I was thinking that if this battery has been at full charge for over a year, is it fair to assume that the capacity is still there and on discharge the full mah would be seen. I know that NiMH batteries would not hold the voltage for this period of time due to self discharge - even the Eneloop.

Sorry if I am way off base here...
Sam
 

SilverFox

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Hello Sam,

The recommendation is to store Li-Ion batteries at around 40% charge. However, there is much (heated) debate over this. Some have stored their cells at full charge for extended periods of time without any noticeable decrease in cell performance. Others keep their cells at 40% until just before they use them, then discharge them back down after use.

I was curious about this and for this test decided to charge up to about 75% and let things go from there.

Tom
 

ofcjim40

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On a side note, how does heat and cold affect the discharge rate. As an example, I have a SF 9P running off of two unprotected 17500's as a backup light in my duty bag (I'm a Cop). My duty bag ends up in my personal car between shifts, so the light will be exposed to the changing environment in a car. So I'm sure at times the temp will be above 110 degrees in the car, etc on a very hot summer day. I usually charge the batteries in this light once a week (it is rarely used). Am I putting the bateries in danger or is this no biggie? Thanks.
 

MrAl

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Hello again Tom,

That's great as the light i use most uses an Li-ion too.

Take care,
Al
 

NotRegulated

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ofcjim40 said:
On a side note, how does heat and cold affect the discharge rate. As an example, I have a SF 9P running off of two unprotected 17500's as a backup light in my duty bag (I'm a Cop). My duty bag ends up in my personal car between shifts, so the light will be exposed to the changing environment in a car. So I'm sure at times the temp will be above 110 degrees in the car, etc on a very hot summer day. I usually charge the batteries in this light once a week (it is rarely used). Am I putting the bateries in danger or is this no biggie? Thanks.

I have been letting my TL3 with 17500's sit in my car overnight every night for months. I am amazed that the charge in the batteries still is maintained and the light works great. Nothing scientific to back this up. Night time temps in the Winter are mid 30's to 40's, and daytime temp (car in covered parking) is 75. Later at home it's 90-100 inside the car. I keep three primary 123's also in the car with the light as well.
 

Brighteyez

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Unless you're leaving the windows wide-open on the car during the day, chances are that the internal temperature in a locked car sitting in the sun during one of those real hot August days, are probably more like 130º-140ºF.

I've always chuckled when people ask me if the cold winters in Chicago were difficult, and I always reply that it was the summers (with humidity) that bothered me most. :)

ofcjim40 said:
So I'm sure at times the temp will be above 110 degrees in the car, etc on a very hot summer day.
 

SilverFox

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I have added the discharge testing data to the first post. In 1 year, this cell had 95% of its remaining capacity left.

Tom
 

changsn

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Thanks Tom, would you infer that storage is not as big a deal as the mfg ers seem to think? Perhaps too big a leap to make on one data point...
Sam
 
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