What is MINIMUN voltage for 18650 batteries to be called "DEAD"?

[Paingamesyt]

Hello guys

I did post 2 days ago on how to safely remove 18650 battery from Xiaomi power bank that had broken charging port and i did remove tham thanks to this great community and also thanks to member @MANIKYATH for the help

Now i wanted to know what is DEAD 18650 battery, what is MINIMUN VOLTAGE to be called DEAD and what are SAFE voltage for this battery? 

Also i want to buy some charging device for 18650 and use these batteries for some devices that uses 18650 

Its great if can someone recommend charging device from aliexpress

 

 

here are pictures from EX-Power bank

 

 

You can see on 1 picture that 1 battery was almost exploded, this was not by me, it was i think manufacturer error, 1 battery was not properly connected, on - side it was disconnected from 2nd battery and did not properly charged or discharged. This powerbank was used almost 7 years and thanks God did not explode or catch on fire  These are LG cells and i think thats why they did not catch on fire. 

 

 

 

On these 2 picture i did test battery voltage. 3 batteries had 2.48v (these are 3 batteries that was together) but one battery had at first 3.07 voltage but later it jump to 4.16v (This battery was supposed to be connected with swallowed battery but did not) i dont know how this battery was not damaged, because minus was not properly connected with 2nd battery. To properly charge or discharge there, battery need to be connected at - and + PROPERLY but on these 2 battery it was not properly connected

 

But most importand, at least 1 battery is saved  thats worth trying  

[mariushm]

A protection IC should disconnect battery once you hit 3v. It's not good idea to discharge below 3v.   

 

With a proper charger IC, those batteries have a good chance of being recovered. Good charger ICs have a pre-charge stage where they trickle charge with very little current until the battery goes up to around 3v, then it switches to higher current charging.

For example, even a cheap half dollar linear charger ic MCP73831 has pre-charge, see page 13 in datasheet : https://ww1.microchip.com/downloads/en/DeviceDoc/MCP73831-Family-Data-Sheet-DS20001984H.pdf

You can buy these chips in various max voltage thresholds, you would want 4.2v as that's the most common.  May want to use 4.1v only if you want to extend the life of batteries by not charging them at 100%.

[Paingamesyt]

15 minutes ago, mariushm said:

A protection IC should disconnect battery once you hit 3v. It's not good idea to discharge below 3v.   

 

With a proper charger IC, those batteries have a good chance of being recovered. Good charger ICs have a pre-charge stage where they trickle charge with very little current until the battery goes up to around 3v, then it switches to higher current charging.

For example, even a cheap half dollar linear charger ic MCP73831 has pre-charge, see page 13 in datasheet : https://ww1.microchip.com/downloads/en/DeviceDoc/MCP73831-Family-Data-Sheet-DS20001984H.pdf

You can buy these chips in various max voltage thresholds, you would want 4.2v as that's the most common.  May want to use 4.1v only if you want to extend the life of batteries by not charging them at 100%.

Thanks for info, this is too much techinal for me to understand it  

 

But just now i did search info about 18650 battery cells and they say: "The minimum voltage for NMC 18650 batteries is about 2.5 volts. A BMS will actively work to prevent a cell from going below 2.5v by putting the battery pack into safe mode. Any lower than around 2.5V, and irreparable damage in the form of lithium plating will occur within the battery.

If your cells run lower than 2.5V for a short period of time, then the amount of damage that happens is minimal. If, however, they are left that low for a long time, it can totally destroy the cells." 

 

so this means that if battery is bellow 2.5v long time then that can damage battery cell and i dont know how long these batteries was 2.48v

This powerbank was last charged 2y ago and just now i decided to disassemble it and see if i can save some batteries. 

 

I will try to charge them at least near to 3v and wait for this charger to arrive: https://vi.aliexpress.com/item/32799915099.html?spm=a2g0o.cart.0.0.361738dazFFfwA&mp=1&gatewayAdapt=glo2vnm

 

I have some charger but i dont trust it, so i will charge battery for 15-30min and leave battery and charger outside just in case it happens something. I think this LittoKala is good so till that arrive i will charge them to 3v

[thiccbeard4linux]

I've charged a battery that was down to about 1.5v and it definitely was damaged (lots of voltage drop).  I wouldn't go below 2.0v, and I wouldn't regularly go below 2.5v.

[Paingamesyt]

Update: 4/5 saved battery BABY ^_^ I have been charging them yesterday for around 5-10min on a charger that i dont 100% trust for safety reason  But it did charge them and they hold voltage to 3.5v (They was 2.48v and charged for 5-10min)

 

So i can say this experiment was succesfull  18650 battery in my country cost 5-7euro ( 2.600mAh unknown brand) but these are LG Cells and they are 3200mAh, they are OLD and probably they are not in great condition but why do i need to throw them when i can use them on something

 

Thanks again to this community and to Mariush for information and help