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Are these batteries damaged?

kolek

kolek

Inventor of the Electron
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Sep 29, 2021
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400
LF280 cells purchased from Amy at Shenzhen Luyuan 2 years ago.
Supposedly her best "Grade A" batteries.
The batteries have never been used.

Using battery charger, charged a group of 6 batteries for the first time to 3.56V.
Now after just sitting for 2 days, the charge on each of the 6 batteries has dropped to about 3.38V.
Is it normal for these batteries to drop that much when just sitting inactive?
 
According to @740GLE after a regular top balance to 3.65V, cells should settle down to 3.45-3.5v.
Assuming 3.45V, that's a drop of 5.5%.

Assuming a similar 5.5% drop starting at 3.56V gives 3.36V, so I guess they are still roughly showing a normal dropoff.

Just didn't expect to see that much of a decline so quickly and concerned because these cells already have 2+ years of calendar aging.
 
What voltage were they at after storing two years? What was the current flow when the charge was terminated?
 
It's very normal for Lifepo4 cells to relax down from 3.65 volts. I've seen perfectly acceptable cells drop lower than yours. Just remember they're is not a linear relationship between voltage and stored energy.
 
NIFE said:
What voltage were they at after storing two years? What was the current flow when the charge was terminated?
Click to expand...
@NIFE
Thanks for responding!

Voltage after storing two years: 3.29V

Max current flow during charging was around 30 amps. When the charge was terminated, that had decreased to about 1 or 2A because the charger had reached the target voltage I had set.
 
400bird said:
It's very normal for Lifepo4 cells to relax down from 3.65 volts. I've seen perfectly acceptable cells drop lower than yours. Just remember they're is not a linear relationship between voltage and stored energy.
Click to expand...
@400bird Thanks for your response, that's reassuring to hear.

Speaking of "stored energy" I've seen some people say it's better not to leave these batteries charged. It's going to be a couple weeks until I'm able to put these batteries into use, is it better to discharge the ones I've charged?
 
kolek said:
@400bird Thanks for your response, that's reassuring to hear.

Speaking of "stored energy" I've seen some people say it's better not to leave these batteries charged. It's going to be a couple weeks until I'm able to put these batteries into use, is it better to discharge the ones I've charged?
Click to expand...
Leave them as is. If the cells are still in parallel, disconnect. Individual cell voltages in a few weeks might be a useful reference.
 
If I need to discharge at some point, could a 100V 200 watt light bulb be used to discharge a single cell or group of 4 cells in series?
 
kolek said:
@400bird Thanks for your response, that's reassuring to hear.

Speaking of "stored energy" I've seen some people say it's better not to leave these batteries charged. It's going to be a couple weeks until I'm able to put these batteries into use, is it better to discharge the ones I've charged?
Click to expand...
Specifically, fully charged. However, one time, for a couple weeks, I wouldn't worry about. Just don't recharge every month just to put them back on the shelf until the next recharge in a month.

Even then, it's unlikely to cause noticeable effects.
Depending on what specific cells you have, they are rated for something like 8 years of daily cycles. Maybe you cut it down to 7. I don't know your use case, but your probably not cycling them every day.
And even then, at the end of the 7-8 years, they aren't dead, they have 80% capacity remaining.
 
kolek said:
Using battery charger, charged a group of 6 batteries for the first time to 3.56V.
Now after just sitting for 2 days, the charge on each of the 6 batteries has dropped to about 3.38V.
Click to expand...
So, you charged the cells, left it to rest for two days and found their OCV to be 3.38V.
Congrats, You just accidentally discovered the fully charged OCV of a LFP Cell at rest. Which is ~3.37V.

This is beyond just normal. This is expected. All LFP Cells show roughly the same behaviour.
 
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