High self-discharge on Sofirn 21700 battery

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SIGShooter
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High self-discharge on Sofirn 21700 battery

I have a Sofirn 21700 that has a high self-discharge. It discharged itself from 3.9v when I packed it away on 5/1 this year down to 2.35v as measured today when I happened to look at it. Before anyone asks it was in a battery storage container by itself so there was no way it could have made contact with anything else.

Normally I’m leery about using/charging batteries that have gone below 2.5v so I’m not sure what I’ll do with it.

I’ve never had any batteries that have self-discharged this much, so I’m wondering if there is something intrinsically wrong with the battery that would cause it to be unsafe to use (disregarding the fact that it was down to 2.35v).

Any care to speculate or offer an opinion?

Thanks Smile

Nachtfeuerzeug
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Just stop using and dispose of it. Some good sales for better quality batteries will come up soon enough. 

Oli
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Even if you found it at 2.9v, in the grand scheme of things the battery is faulty and it’s not worth messing with.

You can't compare the big flashlight in the sky to the little flashlight in your hand.

SIGShooter
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Oli wrote:
Even if you found it at 2.9v, in the grand scheme of things the battery is faulty and it’s not worth messing with.

Yeap….I’m sure there are reason for such a high discharge and none of them are any good I bet Facepalm

My safety and those of others is worth way more than a $5 battery.

alpg88
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yea, it is shot, throw it away,. or take it to a shooting range, and make us a video, lol jk.

SIGShooter
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alpg88 wrote:

yea, it is shot, throw it away,. or take it to a shooting range, and make us a video, lol jk.

I don’t think the range master will be too happy if I did that haha. In the old days I used to do a lot of shooting at friend’s farms near San Francisco but they’ve all turned into apartments and strip malls, otherwise I could do it there.

I miss those days when it was easy to go out and shoot to my heart’s content Sad

Serlite
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I also experienced this with a Sofirn 21700 (5000 mAh) – I tested the voltage for a couple weeks after charging and watched it steadily drop from full to empty.
It was even warmer to the touch than my other batteries sitting at room temperature, which basically confirmed some kind of internal short.
Still waiting to properly dispose of it, but now that it’s fully discharged there’s not much danger in keeping it around.

I suppose that’s just the lottery we play when we use these pretty good but cheaply-manufactured cells.

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Serlite wrote:
I also experienced this with a Sofirn 21700 (5000 mAh) – I tested the voltage for a couple weeks after charging and watched it steadily drop from full to empty.
It was even warmer to the touch than my other batteries sitting at room temperature, which basically confirmed some kind of internal short.
Still waiting to properly dispose of it, but now that it’s fully discharged there’s not much danger in keeping it around.

I suppose that’s just the lottery we play when we use these pretty good but cheaply-manufactured cells.

That’s for sure about the lottery God being in play. With re-wraps one never knows what one is getting, even batteries in the same order may be different under the skin.

Since it’s down to 2.5v I’ll just short it across a resistor and by tomorrow it should be as close to 0v as possible.

habeba86
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I had the same issue with a battery of theirs.

Correllux
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Well that’s a bummer to hear…they’ve seemed to be supplying such decent cells. Can you guys tell us when you received the cells and where you bought them? Maybe it’s a batch or something and not a more widespread issue. Do you have any older-ish Sofirn cells to visually compare with (i.e. have they perhaps changed cells for some reason)?

SIGShooter
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Correllux wrote:
Well that’s a bummer to hear…they’ve seemed to be supplying such decent cells. Can you guys tell us when you received the cells and where you bought them? Maybe it’s a batch or something and not a more widespread issue. Do you have any older-ish Sofirn cells to visually compare with (i.e. have they perhaps changed cells for some reason)?

All my Sofirn 10 18650’s have been fine and don’t show any more voltage drop than any other 18650, which is to say nothing that is noticeable.

I have 2 of their 21700 batteries, both of which are identical in appearance. My bad one came with a light I bought earlier this year while the other one came with a light bought last year, both from their Amazon store. Maybe it’s just an issue with the 21700’s and not the 18650’s? Who knows, but Serlite’s battery was also a 21700.

It was clear to me that the bad battery was behaving oddly. Off the charger it dropped more than it should have after a day, and then keep dropping daily even when it should have stabilized afterwards. I made a note to check the voltage every week or so but then of course forget to do so Facepalm

The problem with re-wrapped batteries is that we don’t know what we’re getting from one order to the next. Plus we don’t know how much, if any, quality control Sofirn or any other manufacturer is spending on their re-wrapped batteries.

habeba86
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Mine was about a year ago. It was a 21700 from a Wurkkos ts30. I assume its the same as sofirn battery.

poohduck
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I won’t / can’t comment on whether batteries are faulty or not. I assume folk here know not to store Li Ion batteries at either extreme (0 or 100%)? For example my lights get used randomly – sometimes not for weeks – so I charge to 80%.

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My 2 Sofirn 21700’s were charged for storage, about 3.7v, so definitely not charged at full or completely drained states.

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Sofirn’s cells are fairly decent from BAK and/or Lishen. I run my own flashlight business in New Zealand stocking large quantities of BAK and Lishen cells and haven’t yet had an issue. I check voltages of every cell before shipping out to customers and also run a discharge test on each batch to confirm authenticity on my CBA.

All cells from the main brands also have cells that go bad randomly, so it’s not something we can suggest the Sofirn cells could be problematic based on a couple reports. I’ve personally had bad LG, Samsung and Panasonic with high discharge from new, but that’s not to say those brands aren’t any good now.

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SIGShooter wrote:
alpg88 wrote:
yea, it is shot, throw it away,. or take it to a shooting range, and make us a video, lol jk.

I don’t think the range master will be too happy if I did that haha.

Just tell him you’re testing out some eerie tannerite. LOL

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Lightbringer wrote:
Just tell him you’re testing out some eerie tannerite. LOL

I planned to use tannerite in my YouTube reviews for the hunting flashlights, until finding out it’s illegal over here. I have the supplies, but can’t mix them.

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Thanks, Sig. I try to check each new cell as well but this reminds me there are a couple I haven’t yet. I think I have maybe 7 or 8 Sofirn 21700 in both 4000 and 5000, couple of which were received in the last six months or so. Just two of their 18650, and a couple of each in the Wurkkos flavors as well. Save for the couple I need to put an eye on they’ve all been stable and seem to be great cells comparable with the 50E that I prefer (I can’t recall now if the 4000 Lishen is on par with the 40T from HJK’s test but seems like it was close). Visually they all look the same to me other than the bottom ring/vent on newer ones…haven’t unwrapped any of them but I too have been assuming the Wurkkos were the same cells. Mine are a mix of Ali and Amazon going back about four or five years, but the majority of the cells came from Amazon since I usually buy lights without cells when shopping Ali (and my Amazon cells/lights are mostly from the last two years I think).

Hopefully a one-off problem cell/batch or something. Three people in this thread now, however.

SIGShooter
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Correllux wrote:
Thanks, Sig. I try to check each new cell as well but this reminds me there are a couple I haven’t yet. I think I have maybe 7 or 8 Sofirn 21700 in both 4000 and 5000, couple of which were received in the last six months or so. Just two of their 18650, and a couple of each in the Wurkkos flavors as well. Save for the couple I need to put an eye on they’ve all been stable and seem to be great cells comparable with the 50E that I prefer (I can’t recall now if the 4000 Lishen is on par with the 40T from HJK’s test but seems like it was close). Visually they all look the same to me other than the bottom ring/vent on newer ones…haven’t unwrapped any of them but I too have been assuming the Wurkkos were the same cells. Mine are a mix of Ali and Amazon going back about four or five years, but the majority of the cells came from Amazon since I usually buy lights without cells when shopping Ali (and my Amazon cells/lights are mostly from the last two years I think).

Hopefully a one-off problem cell/batch or something. Three people in this thread now, however.

Yeah hopefully it’s a rare issue but if someone is actively using a cell like that in a light how would they even know? The voltage drop is low enough that they would just think it’s due to using the light, at least that would have been my thought.

It’s only when the battery is stored and then checked before usage would it become clear that something is wrong.

The fact that the battery isn’t overly discharge in this scenario doesn’t mean that there’s no defect in it. How serious that is, if it’s even serious, is all speculation I would think.

Correllux
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Just part of the li-ion world. I do worry about that sometimes as we see more and more of them being sold on Amazon and such, and I have yet to receive a single light where anything appreciable is said in owner’s manuals about what we know as basic lithium safety/responsibility. The more e-bike and scooter fires we see, and the push from Samsung to label cells as “do not use, period” and restrict aftermarket access, the more important this basic education is becoming, imho. I guess it’s learn or be dumbed down by using only protected cells that have full protection circuits in them, which seems to be the way things are going with many brands. Nobody really takes it seriously anymore unless they short out a cell and catch a whiff, or if they actually witness a venting or something, and with all the new interest via this forum and youtube and reddit, it doesn’t seem that many take the time to teach new folks about it, either.

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Yeah, I see this all the time in NZ, so many customers of mine already have existing lithium flashlights yet are shaken by learning that they can explode if misused. I include a printout on battery safety with each flashlight and also have a page on battery safety I’ve copied and slightly tweaked from BLF.

I remember one guy complained about his Convoy C8 blinking at 2.8v, I learnt he ran all cells virtually to 0v each time in his vape and was annoyed he couldn’t do the same on his light.

One thing I never see mentioned is battery safety when mounting a flashlight on a rifle, button top must be used otherwise one risks the spring denting in the top and blocking the relief vent. I’ve had people questioning why I state “button top only when mounting” and after I explain a cell could potentially explode if that vent can’t open, I never hear from them again, probably went back to AA’s.

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I’m never amazed by people who do dumb things and/or don’t bothered to read up on things that are potentially dangerous. It’s just the world we live in now where people assume everything will be safe and that they’ll be taken of because of…….reasons.

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Lotta people have the cellphone mentality. Ie, run it down ‘til it shuts off on its own, plug it in to recharge, rinse, repeat.

People who get “protected” cells assume the same. After all, it says “protected” right on the tin!

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