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How hard it is to kill an unprotected cell?

Skylumen

Newly Enlightened
Joined
Sep 14, 2010
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0
2 months ago I connected a nearly dead unprotected laptop pull 18650 to a XML LED. Still glowing today...:whistle:





Let see if it last until New Year. Current voltage is 2.25V
 

eekazum

Flashlight Enthusiast
Joined
Mar 27, 2016
Messages
1,050
2 months ago? And it was nearly dead at the time? daaang. Check the polarity after you are done :)

Are you planning on trying to recharge it?

I'm trying really hard not to bring up wimmer...
 

BootsAndCats

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Mar 11, 2015
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USA
I thought over discharging a LiOn cell is dangerous, especially an unprotected one...
 

eekazum

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Mar 27, 2016
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1,050
I thought over discharging a LiOn cell is dangerous, especially an unprotected one...

"Dangerous" meaning, it -could- damage/kill the battery. I'm no expert on this but I doubt the battery will leak, explode, or try to steal your firstborn if you let it slowly drain past 3v or below.

Just like putting a 5lb weight on an everyday kitchen rubberband, it could snap, or not. It could stretch to the point where it doesn't snap back anymore, or it can take the weight no problem. The point being, if you LEAVE that weight on that rubberband, eventually it WILL stretch or snap, destroying the rubberband. But no harm to you, the weight, nor the future president of the USA.

I also heard that overdraining a li-ion battery could actually reverse it's polarity and that trying to use or recharge such a battery is like, well, putting it in backward. That doesn't sound like fun results...
 

Bdm82

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May 27, 2016
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Illinois
Draining isn't really the danger. Recharging it is.
Being below 2.5v, this battery is done after this experiment. One And Done.
 

kaptain_zero

Enlightened
Joined
May 31, 2010
Messages
220
Draining isn't really the danger. Recharging it is.
Being below 2.5v, this battery is done after this experiment. One And Done.

You are correct, draining is not the real danger, it's attempting to recharge it that is! It's not that it will melt down with flame if you recharge it... it's that you do not KNOW what it's going to do, it's what it MIGHT DO.....

And worse yet... it might not get around to venting with flame until the second, third... etc.... time you charge it. The cell has been compromised, when it will fail is a variable that we cannot predict.
 

lampeDépêche

Flashlight Enthusiast
Joined
May 15, 2012
Messages
1,241
I see that ZL says this on their 18650 lights:

Builtin over-discharging protection (2.7V cutoff)
or:
Built in battery protections with continuously monitored temperature, current, and voltage, plus a (2.7V) low voltage cutoff

If 2.5v is permanently damaged and dangerous from now on, is 2.7v cutting it a bit close?
 

Bdm82

Flashlight Enthusiast
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May 27, 2016
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1,000
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I see that ZL says this on their 18650 lights:

Builtin over-discharging protection (2.7V cutoff)
or:
Built in battery protections with continuously monitored temperature, current, and voltage, plus a (2.7V) low voltage cutoff

If 2.5v is permanently damaged and dangerous from now on, is 2.7v cutting it a bit close?
If you Google your battery model number and "spec sheet" you can find the oem spec sheets stating min voltage cutoff. That is the point you should absolutely never dip below. I've seen anywhere from 2 to 2.8, most in the mid to lower half of that.

That said, most of us don't push past 3.0 very often. My understanding is that when the V gets low the A pull in many lights goes up to compensate, working the batt even harder when almost empty. The runtime left between 2.5 and 2.9 is small; not worth trying to push it.

So 3 is a good, safe, easy to remember number for me so I don't have to remember whether a batt was spec at 2.5 or 2.7, etc.
 

MAD777

Flashlight Enthusiast
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Jul 31, 2015
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White Mountains, NH, USA
Also, when you remove a battery from a light under load, the voltage immediately begins to "recover." By the time it gets to the charger, the voltage reading is a few tenths higher than it was in the working flashlight.

In other words, if the reading is 3.0v, then it was in the mid to upper 2's when under load.
 

A.marquardt

Enlightened
Joined
Sep 30, 2014
Messages
308
Location
Alaska
The newish 3500mAH batteries die pretty easy. I had 4 of them in my TMo4vn (which has a constant, blue LED power available light) and have killed 3 of them dead dead dead. These are the first batteries I have ever run across that simply die from overdischarging.... They were NEW too, so I'm not very impressed with them.
 

Illum

Flashaholic
Joined
Apr 29, 2006
Messages
13,053
Location
Central Florida, USA
A.marquardt, if its an abrupt cutoff, thats the PCB working. I know of no unprotected cells that has an abrupt cutoff, unless the leads were severed.

Considering that you can light a very low Vf LED like an XP-L where you can see the glow in the dark just by using two lemon halves.... I don't think this test is really useful for anything. if you heat the cell somewhat using a blowdryer, it'll give you a wee more light. Just don't recharge it afterwards
 

lampeDépêche

Flashlight Enthusiast
Joined
May 15, 2012
Messages
1,241
Considering that you can light a very low Vf LED like an XP-L where you can see the glow in the dark just by using two lemon halves....

Somewhere on CPF at this very moment, a visionary inventor is trying to figure out how to power 6 XP-L's on a crate of lemons, and still make it EDC'able....
 
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