I would, yeah. Some may tell you that it’s possible to recharge them. But personally I would never feel comfortable with those cells again after they have spent such a long time at such a low charge.
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Thx. I guess it is time to call the time of death on January 27th, 2025, 2200 hours
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Absolutely, this is how i got my test cells. Try not to pop the cans as that electrolyte is nasty still. I hit them a few times testing and then scrap em. I started a little notebook with settings so i need fewer and fewer test cells but always have a couple around
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Excellent idea. Thx
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They were probably okay but it’s usually just not worth taking the risk. The datasheet doesn’t mention any voltage below 2.5V, even for over-discharge recovery.
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Half of those groups are still at or very near to 2.5 V, so they should be fine, right? Maybe I’m just overly lax, but three groups (3, 9, 11) are perfectly fine, three (4, 7, 10) are so close to 2.5 V that I’d have absolutely no issues using them again, four (5, 6, 8, 12) are in the category of questionable where I wouldn’t tell someone else to use them, but I probably would, and only two (1, 2) really concern me.
Am I wrong that there is absolutely no issue with a cell resting at its minimum voltage for an extended period? I’ve seen several papers that show that is actually where batteries degrade the least when stored, as long as they don’t go under. Also, I have a hard time imagining that sitting at 2.5 V for 2 years is fine, but being at 4.475 (EDIT: this was a typo as clarified below, but I don’t want anyone to think 4.475 V may be a reasonable cell voltage. I meant 2.475 V) a for a few months trashes the cell, but I could be wrong on that one. I’d imagine that, given these probably saw a constant draw, they haven’t been below 2.5 V for long.
Edit: Also, I’d argue, since the specs sheet says “2.5 V” for the minimum, that 2.45 V is still in spec. If they meant it shouldn’t hit 2.49 V, then they should have written 2.50 V minimum, and that is a first year of college mistake.
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I think I’ll use the ones that are at 2.5V and above for small projects, I’m not feeling lucky with the rest. I’ll take the L for this one 
You’d have to bring the cell back up to 2.50V frequently though.
4.475V is incredibly abusive and the cell could be ruined by that. Higher voltages speed up the parasitic reactions that damage the cell. Going over 4.250V really starts speeding things up.
Technically you’re correct. But the trailing zero, or zeros, are often omitted for clarity and are just assumed.
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4.475V is incredibly abusive and the cell could be ruined by that. Higher voltages speed up the parasitic reactions that damage the cell. Going over 4.250V really starts speeding things up.
Whoops, that was a typo on my part. I meant 2.475 V.
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Also, as far as
Technically you’re correct. But the trailing zero, or zeros, are often omitted for clarity and are just assumed.
I wouldn’t get pedantic about this in more casual communications, but to me, if you’re writing a technical document, as the datasheets for these cells are, you should absolutely not be shortening things like that. If you mean it should not reach 2.49 V, your datasheet should unambiguously make that clear. If your datasheet is written in a way that can reasonably be interpreted to mean 2.45 V is okay, and someone has an issue because of that, that is on the author of the datasheet in my book.
I’m not actually sure what the right interpretation is, which is concerning to me, TBH. As I intended to say, I wouldn’t think 2.475 V for a bit would be a huge issue, but I haven’t read a lot about what happens when cells are slightly over-discharged. If they do mean it shouldn’t ever drop below 2.500 V, it is quite an issue in my opinion to write 2.5 V with no trailing zeros in a technical document.
2.475V resting voltage is technically more abusive and causes more damage than 2.500V. But it’s probably not so in any meaningful way that would be noticed or perhaps even reliably detected.
IMO it would be chemistry dependent. Even cell dependent.
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It’s a cycle life issue so there’s no real hard limit. Some datasheets discuss recovery from even “1V” over-discharge and others mention to never let the cell drop below “2.0V” or otherwise performance cannot be guaranteed.
So the low voltage spec, to whatever precision it’s brought to, is really more of a spec to not go below if the spec’d cycle life is desired.
But to make things complicated, some cells have their anode current collectors start to dissolve as you drop below the low volt spec. The lower you go and the longer you are there the worse the damage is.
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Ok hummie
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I my opinion, we should not forget that cells are actually a chemical power source.
What does this mean is that all of the boundaries like 2.5/4.2 are not exact. They describe levels at which chemical processes start happening at a noticeable speed + small margin. Let’s say we are speaking about rusting process. It start slowing down when humidity drops down to 70. Nothing rusts in desert, but process continues even at 10% humidity but in a really slow pace.
So voltage levels are specified by manufacturers as safe ones. It means that you can but you should not exceed 4.2v for example. If you monitor cells during balancing you might find out that it’s voltage can be 4.21 or 4.22. And when charging finishes it settles down to 4.20 by balancer.
So the higher the voltage above 4.2, the faster the cell will degrade in an exponential way. Until it reaches the voltage so high, that speed of degradation chemical process will be sufficient enough for cell to catch fire.
On the other hand, this means that cells degrade at 4.1v too, but much slower than at 4.2v.
The same applies to the bottom border. The lower it goes the faster it destroys itself.
That is why cells are stored/shipped at 3.5-3.6v, just to move it’s voltage as far from critical levels as possible.
Edit: so your thoughts are correct. It is not a big deal that cells dropped to a 2.4-2.6 region. And those cells that dropped significantly further could be damaged even earlier. Not only they are dead, they are unsafe anyway.
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What’s making them unsafe?
I would assume that they have been “aged” in a way that significantly degrades the lifespan and output characteristics in a way that cant be reasonably quantified. I don’t have the primary data needed to make informed predictions.
What the failure mode is and how to safely accommodate that isn’t established or worth establishing from a financial perspective. The manufacturer deemed it was of too little value to determine how the cell reacts or it was determined that the way it reacts to being subjected to these conditions creates unnecessary liability. As I understand the manufacturing process, I BELIEVE the cells come off the line at a low voltage possibly in the 1-2v range. There is some anecdotal and non sited source for this but i don’t remember where i got the information or if it is valid.
Its simply “there be dragons” and no map. If there is a process to revive cells after being under voltage, small manufacturing differences could change this process and it isn’t being tracked or accounted for afaik.
You could assume that because the discharge curves all converge at 2.5v that this is the lowest possible voltage that the chemical reactions inside the cell can store power that can be used - as in this is the point at which there is enough chemical/electrical potential difference that the cell can move the ions around usefully. Below this level, the wattage applied to the cell SEEMS to not store any useful energy but POSSIBLY is just helping organize the chemistry and ions into the correct arrangement in order to store power.
There are references on some ?samsung? Cell spec sheets that reference 1v as an absolute cutoff and that pre charging at specified low current until the cell hits a certain threshold voltage and can then be charged normally. If this is applicable to a cell halfway through its cycle life or not isn’t established i.e there be dragons again.
I refuse to offer advice on a subject i haven’t got enough understanding in to know what i don’t know. Ask me about ac/dc systems covered by the NEC and i have experience and knowledge to set you up for success or have a good working knowledge of what is beyond my expertise 
. With batteries i have enough experience to know what I don’t know and how to make safe choices within that environment and to know i am not an expert, but an amateur and applying best practices without full working knowledge
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Your statement regarding safety was pretty final in its conclusion so I was just curious what it was based on. Thanks!
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Hey guys, hope you dont mind me asking -
I’m trying to hot rod some batteries for my Milwaukee M12 2563 impact wrench, as it seems to like having more juice available, but fuck paying 80 bucks for the OEM milwaukee 5.0 HO batteries.
I’ve found some kits for the casing, PCB and nickel tabs, and I’m probably going to buy some Molicel P30B cells to use in them. However, i have no clue what spotwelder setup i should get. Given that this is a pretty simple project, im not looking to spend too much. Will probably just use the spotwelder for this and other small projects, I’ll leave the full esk8 batteries to my regular builder 
Any recommendations on that, or in general for the project and/or any other tools/materials i should buy? Also will gladly take input on if theres any other cells worth considering haha. Unfortunately, im stuck with 18650’s so no fancy 21700 fun stuff.
Battery case, pcb, tabs
https://a.aliexpress.com/_mKF2Pzt
P30B cells
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I currently have the community spotwelder, it would be €35.5 to ship to the states.
But I have some more cells arriving next week though so if I could keep it 7-8 more days it would be great sorry.