A sure way to check for fake cells

Overclocker

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Here's a good way to check by matching the discharge curves from here: http://lygte-info.dk/review/batteries2012/Common18650comparator.php

MzMpWUE.jpg


Obviously this requires a way to graph the discharge curve of your test cell, in this case the Samsung 30Q. Shown here is the iCharger 106B+ via USB (to Logview). Using sense wires to the balance port is recommended.

UgsqjgD.png

(reference 30Q curve from lygte-info.dk)

Now log the data on Logview. Then plot the data as voltage vs capacity on Excel or whatever. Then stretch the image to match the gridlines on the reference graph:

gheJNcS.png


Then combine the images:

gQkzSxL.png


Here my test cell performs just slightly better but it does follow the reference curve extremely well, even down to the characteristic "hump" near the 3.9v mark. So we can conclude that it's legit.

[Moderator edit to fix title]
 
It's pretty incredible that the cells follow the discharge curve so closely. Decisively not fake.
 
That's an excellent correlation between the two curves considering the icharger isn't a precision instrument and the differing/uncontrolled environmental conditions of the test.
 
The iCharger is actually a pretty precise instrument. I went to go calibrate the voltages on mine with a high precision voltmeter and was surprised that the factory calibration was nearly as perfect as it could get. It's part of why i always recommend it for battery testing.

Nice thread by the way.
 
Is there any way to check for fakes if you don't have a charger/discharger? Could I take it to an electrician?

I bought a few 30Q cells and they have a suspect sticker on them, not the printed dot label that you normally see.
 
How many legs does the positive terminal have?

If it's not 3, then you've got for sure a fake cell.
 
I've had some inr18650-25r greens cheap £2.29 each and they are missing the stamp on the bottom and the cans don't have any markings on either.
They test well though which has throw me as they measure up on capacity, but they are weighing in at 46.3g not the 45g max that sumsung say is the max.

When I tested them on a mc3000 I had it set to cut at 2500mah which means its missing the end of the curve i'm retesting them now to get a better graph but what are your initial thoughts?
Regards
Dave
Updates with full discharge test

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