Lowest safe voltage vor LCO batteries

I bought some second life Lithium Cobalt cells. (43Ah pouch cell beasts)
They all have reasonable voltages between 3 and 4 volts. But that is just hiding an ugly truth.

Quite a few of those cells had old voltages written on with felt tips which were below 2V. Voltages like 1.7V

To be honest, that kind of voltage freaks me out! If those where my RC mode LiPo cells I would have considered throwing them out after such level of neglect.
But I don't know what's really safe and what not. And those cells are certainly too expensive to throw half of them out.

When do LCO chemical layers break down?

I think Samsung wrote somewhere that the absolute min voltage (for their cells anyways) is somewhere around 1.6V.

You could always buy yourself a capacity meter to check all the cells. And then sort the cells with very close or matching capacity in groups.

I test cells with this thing:https://www.ebay.at/itm/ZKE-EBC-A10-Li-Pb-Battery-Charging-Capacity-Test-Power-Performance-Tester-Charge/162099719284?hash=item25bde56c74:g:FYAAAOSwepJXWt4J

You might want a more powerful version:https://www.ebay.at/itm/EBC-A40L-5V-40A-Battery-Tester-Lithium-Polymer-Power-Battery-Discharge-Charge/262613463048?hash=item3d24fb7008:g:8jMAAOSwJ~RZr8Sz or https://www.aliexpress.com/item/EBC-A40L-high-current-battery-capacity-tester-20Acharge-40A-discharge-battery-line-graph-Battery-tester-Battery/32370809953.html

Thanks. I might have just dodged the bullet there.

Those are some beefy testers indeed. I played with the idea of using a rc model charger but that would take way too long. :lol:

To be honest I would avoid any cells with a resting voltage less than 3 volts like the plague.

When LiCo cells are shipped they are sent at about 3.89 volts, which is probably about half-charged. I would never let them dip below 2.7 volts under load. At the end of the discharge, a cell might 2.7 volts under a nominal load, but recover to 3.4 volts with no load. Consider that cell empty.

In my experience, Cells that have been slowly discharged because of something like a BMS system’s idle current draw to voltages of 1.5-2.5 show essentially little to no effect from that event, depending on how long they stayed at that voltage.

Yea, it doesn't look good. I took some measurements a few days later. Just a few cells.
The ones with low voltage history lost over a tenth of a volt. The other ones are stable.
Looks like it already got dendrites that leak current internally.

It's not so bad. I got a plan B that was cheaper and better. https://endless-sphere.com/forums/viewtopic.php?t=90395
But I have to figure out what to do with my 24 cells for 950 EUR now. Maybe I can give them back to the guy who sold them to me...

If you think you can get your money back then you certainly have a claim - you were sold scrap batteries as working ones