# Minimum Li-ion discharge voltage?



## crosstalk (Feb 22, 2012)

We have been running a device (not a flashlight, sorry -- but it has a very low current draw (battery life of weeks/months)) on a Tenergy RCR123A battery (I know "RCR123A" is a bit of a misnomer). This cell is protected.

I took it out recently, after the low battery alert (which had been going off for weeks) suddenly became much more aggressive. I measured the voltage over the cell to be 2.41-2.43 volts.

I recall, from a couple of years ago (last time I really read CPF), that 2.40 volts is the minimum discharge voltage before a Li-ion cell must be thrown away. I also recall reading a mention that some protection circuits will fail to kick in when the current draw is sufficiently low, so I'm afraid that this cell might be dead.

I'm having trouble finding the 2.40 volt number to verify that my memory is correct, however. Could someone please confirm this or correct me? Am I fine recharging this battery?

Thank you for any help.

EDIT: My newlines mysteriously disappeared on submission -- adding them back in.


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## mvyrmnd (Feb 22, 2012)

2.7V is usually the safe cut off point.

2.4V discharges will shorten the life of the cell, but probably not result in 

Charge it now 

If kept at really low voltages (<2V) for any length of time (days) then the battery will be unsafe.


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## HKJ (Feb 22, 2012)

crosstalk said:


> I also recall reading a mention that some protection circuits will fail to kick in when the current draw is sufficiently low, so I'm afraid that this cell might be dead.



I have never seen this and believe that it is probably a misunderstanding.
I.e. if you drain a battery with 1A until protection kicks in and then reset it and measure the voltage it might read 3.6 volt. But if you drain a battery with 1mA until protection kicks in and then reset it and measure the voltage it might read 2.4 volt. This is not because any fault with the protection (This can be discussed), but because the battery does not recover when drained at a low current.


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## Mr Happy (Feb 22, 2012)

It is probably not necessary to throw it away, but it would be a good idea to heed the low battery warning next time and recharge it sooner. Try not to let it go below 3 V if you can help it.


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## crosstalk (Feb 22, 2012)

Thank you, that's all I need to hear.


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## snakyjake (Feb 22, 2012)

Callies Kustoms says 2.5v for their 18650.


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## CKOD (Feb 22, 2012)

snakyjake said:


> Callies Kustoms says 2.5v for their 18650.


http://industrial.panasonic.com/www-data/pdf2/ACA4000/ACA4000CE254.pdf


2.5V is the voltage under load (590mA in the case of the panasonic 3100mAh cells linked above, that Callies uses) Also note the capacity vs cycles chart to the right. If you read 2.5v while under no load, your under load voltage will be much lower, and you're exceeding the manufacturers specs and expect your capacity vs cycle graph to be much more steep 

Also, Panasonic NCR18650 cells are unusually low with their 2.5v cutoff, 2.75 is more normal among 18650s Under no load, 3.0v is pretty much empty with not a significant amount of useable energy left.


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