Cell capacity decreasing over time?

cadric

cadric

Member
Joined
May 3, 2018
Messages
110
Hi all,

I started collecting cells in Mai 2018 after I understood the recycling of old Laptop Batteries.

Now I started to build my packs and I realized that the cells I tested in the early days have lost a lot of their capacity.
For example, a cell initially tested about ~1500mAh between 4.0 V to 3.5 V now has only ~1150mAh.

Is it because of aging, or what can be the reason?
When I stored them they had about 3.5 to 3.7 Volt, which they still nearly have, so they did not discharge by themself.

Does it mean, I should not let them rest for such a long period?
I don't expect them to lose their capacitiy when they are in use, especially only between 3.5 and 4.0 Volt, or do they?


regards

cadric
 
It seems unlikely to me that they would lose that much capacity just sitting.
Have you considered other variables?
Are you using the same charger, capacity tester, same conditions?
Is the tester ok? I have seen some posts about testers reading the wrong voltage.
What does a test from 4.2v down to 3v show?
I have noticed a drop in capacity when testing cells at colder temperatures compared to warmer temperatures.
 
As Oz told, it's very important to test in the same conditions (tester, holder, temperature, etc...). Whatever, capacity drop from 1500 to 1150Ah in 4.0-3.5V range seems too big to me too.
 
Hi,

and thanks for your response.

For Charging and Testing I use two Sky RC 3000.

Ok, the first tests with this cells I did in November 2018, the shed was not warm at that time if I can recall correctly,
so maybe it is because of the difference in temperature?!
But that would mean, it was colder on the first check but the capcity was much higher, which also does not make sense.
So next step is to check with cells I did last year in June/July to see if there is any difference.

regards

cadric.
 
Could you have been using different rate of discharge during previous testing compared to now?
Are both skyrc devices giving the same results as each other?
 
Oz18650 said:
Could you have been using different rate of discharge during previous testing compared to now?
Are both skyrc devices giving the same results as each other?
Click to expand...

no, always charging and discharging with 500mA only.
yes, they both are in the same range, with a little difference but not to mention.
 
For storage is temperature very important.
Also the voltage, the optimum voltage storage would be 3.4v.
 
Is this happening with a particular brand or model of cell? I experienced the same thingwith sony green cells but others using sonys didnt have the issues I experienced.​
 
jm1 said:
Is this happening with a particular brand or model of cell? I experienced the same thingwith sony green cells but others using sonys didnt have the issues I experienced.​
Click to expand...

NO, cells are mixed, no special brand.
 
cadric said:
NO, cells are mixed, no special brand.
Click to expand...

You say that the cells have originally tested at ~1500mAh between 4.0V to 3.5V.
First of what was the original mAh rating of the cell?
Second what was the IR of the cell? (Proper IR measurements can only be done with a 4 wire kelvin tester such as a YR1030)
If you are testing a 2800mAh cell and you are getting 1500mAh that cell has degraded to 53.57% of its original capacity.
I would also venture to guess that the IR of that cell is in the stratosphere so the loss of mAhs on the second test after sitting would not be a surprise to me.

Wolf
 
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