I've bright LMR batteries back from almost a zero voltage ...(Hard on the charger ) But what's the lowest 18650 L-ion.lithium cobalt... that anyone has successfully revived ?
My lowest was 0.6V Sanyo salvaged cell using hobby charger.
Gave a small charge @0.1A (fully monitored) until it reached 2.7V, the charge CC/CV per normal.
Managed a consistent 1800mAh after that @1A. No internal damage! Sanyo has some really good cells.
Have a UF 18500 at 1.45V that would not take a charge so I zapped it with 7V at 1A until it was up to 2.75 then charged it normally on UF charger. Now it’s at 4.1. We’ll see if it frankenliny lives.
I’ve had laptop cells charged to 4.15V to 4.19V from as low as .7V. However, in my experience the the charged voltage is not a good indicator of the health of a cell. I’ve had old cells charged that to 4.19V only to fail my SC600 5-minute turbo test.
When the cell is exposed to a sustained load, (1.8A on SC600’s turbo), a good cell will finish the 5-minute. An ‘unhealthy’ cell will drop to ‘high’ from turbo to, in some cases, even less than a minute. But these ‘unhealthy’ cells may still be useful on light load lights.
Right around .6 volts. Shorted it in parallel with another fully charged lion and that brought the voltage up to 2.5 and then I just charged it normally from there.
One should NEVER, EVER attempt to salvage those low voltage cells. Once the voltage goes below around 2V the chemistry can become unstable. The cells may appear to be OK, but their chances of spontaneous unprovoked combustion, fiery death, horrible mutilation, etc greatly increase. It’s just not worth it. Personally, I would never attempt to salvage a cell below 2.5V
I’ve had NiMH discharged to –0.2V (yes, minus 0.2). It still charged up fine, but it’s self-discharge has increased greatly.
I had one eneloop go down to the same point and I charged it and it is still in use. I <3 eneloops. :D
@Texaspyro.
You are definitely right. It is very dangerous because when you discharge it that far their may be a permanent chemical reaction that makes it so they cannot charge. However for the hobbyist I think it is fine, I do this outside right next to an ammo can full of sand with a fire extinguisher and a gas mask sitting next to me.
Right on 0 volts …
Success rate from 0 volts = about 50% , some come back , some are never right again …
In about 1 week I start my recharge cycle [ recharge all my batteries ] , so then It will be time to see whats holding voltage and whats not …
I may have 2 suspect 18650 … Last time I charged all the cells , I may have removed 3 from the collection …
Me too . . . but it was the protection circuit.
Nope, it is NEVER fine. One thing that under-discharge/over-charge can do is cause metallic lithium to plate out of the chemistry. This can lead to disaster. Charging a dead cell can lead to a series of reactions that can cause the cell to get very angry at some random time in its future. It may never happen, it may happen instantly, but it is just not worth the potential risk. Think of a damaged cell as some WWII bomb that has been buried for a few decades. It’s not something that you want in your basement.
I don't suggest trying to salvage or charging anything under 2.5 volts either unless they are lmr .
I just ran across some cells lower than I've ever seen laptop cells ..actually they were Purple 17670 panasonics from my own sony laptop pack..A pack i opened up about 5 years ago and thought about rebuilding ..It was cheaper to just buy a new computer . The cells were absolutely dead .034 volts ...Only one over 2 volts ..
Have too many good batteries to mess with dangerous junk
I have some direct experience with the subtle wonders of salvaging dead lithium cells. I was testing a new charger and fed it some dead cells. They apparently charged just fine, but I knew the dangers and left the cells outside in a ceramic planter for later destructive disposal. They were still OK a week later when I passed by them. A couple of weeks later I went to get them and one had cooked off, and rather impressively from the carcass.
Another time I was charging some 0V A123 LiFePO4 cells, a MUCH safer chemistry then LiCo/LiPo. Over half the cells were just fine and I still use them (always stored in fire safe). Most of the others would not charge or had a very fast self discharge. I put one cell that mostly charged in the reject pile. The next day I went to destroy the duds and that cell was now too hot to hold. It stayed hot for another day, but never ruptured or flamed.
PLEASE, just don’t mess with duds, no matter the chemistry… it ain’t worth it.
So you think it will be safe too recharge an IMR18650 thats been at 1.48v for a couple of weeks?
Nope…
Heh - mine was eneloop too. But now it’s more like generic 2000mAh NiMH, loses 50% charge in a month. 
When the voltage drops too low the protection circuit kicks in , but this time it was unprotected cells [ so 0 = 0volts ]
Some times to protection circuit dont want to fire up , then it gets tricky …
Last time I tossed one protected cell , and two unprotected …
So this charge cycle - Starting tomorrow , might see one or two more 18650 discarded