Don’t be upset. It’s just a question. Does my statement above include all the nuances?
It will likely degrade its capacity and could bring potential long term issues with maintaining even balance in a pack, ESPECIALLY if the cell was discharged down that low instead of just passive parasitic draw.
- and add a fucking disclaimer that doing so is at the users own risk and they should consider the potential outcome of a battery fire.
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Also charging a revived cell has an increased chance of a thermal runaway.
Anyone noticed that the only people that suggest reviving dead cells (below 2.5v for a long period of time) are also some of the least accomplished members of this forum?
And that the opposite is true of the people suggesting not to revive dead cells?
It’s actually the other way around…
A slow parasitic draw (uA to mA) results in the cells spending the longest time at a too-low voltage.
Discharging down low under load happens much faster and results in the cell’s voltage bouncing back up once the discharge stops. With the increased (at low charge levels) internal resistance causing a lot of voltage sag the bounce-back can be considerable, often 0.5V or more. This can result in the cell’s resting voltage being near or over 3.0V even if discharged down below 2.5V. The higher the discharge current level the larger the bounce-back.
A slow discharge will result in less bounce-back but will still end up at a higher resting voltage than that caused by parasitic current draw (assuming discharge down to the same voltage for both scenarios).
Disclaimers are a great idea if approaching or exceeding any datasheet limits.
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When talking about reviving a cell though, youd likely be discussing the context of buying a salvaged pack, where its presumably been sitting stored at that low voltage no? In that case, the time spent at low voltage is an unknown, and youd just have maybe the sellers word to know how it got to that voltage - in that case, wouldnt a case of it having been abandoned be better than it having been drawn that low?
Definitely not, for the reasons above.
Discharging too low is only for a very short time if the bounce-back is above 2.5V. Otherwise it’s only until the pack is recharged for a few minutes.
A pack that has over-discharged in storage will almost always have been sitting at a too-low voltage for longer than that. Just the shipping to us would take days and that’s longer than most any pack would be sitting at too low a voltage after being used (if bounce-back wasn’t high enough).
The over-discharged (parasitic draw) from a vendor would probably have been at too low a voltage for months or longer.
But maybe I’m misunderstanding you and the scenario you’re describing?
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Im thinking of two paths leading to someone trying to salvage an overly discharged pack -
Situation A would be loose cells or maybe a complete pack that was originally at storage voltage and was just left alone, parasitically drawn to say, the theorhetical 1V or so.
Situation B would be a device malfunction or other fault, prior user abuse or otherwise with a poorly maintained battery, that actually got discharged to a 1V steady state somehow - not just a sag to 1V that would recover.
Presumably between these two, the former would be preferable if the time spent at low voltage is an unknown right?
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Back to building:
I’m making another battery for a bike like this but will use the aforementioned molicel p42s. They come without any covering on the cells, or at least it slides right off and doesn’t even cover the cell, and I want to re-cover them. How is that best done? Try to heat shrink on the typical vinyl(?) stuff with a paper donut under? That sounds tricky to get right and don’t like the idea of getting heat on a cell if not needed.
Then I’ll pot them like this
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not at all concerned about chargine a cell back up that’s been heavily discharged
advises a newbie to open a water damaged pack
uses siperglue to bond balance leads
scared about using a little hot air on the cell to heat shrink
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Not enough info to say.
Sounds like Situation B’s pack was discharged faster than Situation A’s pack (which reduces time at too low a voltage) but was abused?
But both packs are now at 1V and we don’t know how long either pack took to get to 1V?
We can”t say that Situation A’s pack is the better choice. It might have sat at 1V for a lot longer and that could be a bigger problem than the damage caused by whatever abuse Situation B’s pack experienced.
For example, Situation A’s pack took two years to drop by itself to 1V. Situation B’s pack was abused which fried some electronics and it self-discharged to 1V in three weeks. We don’t know if the abuse has increased the risk of using the Situation B pack more than the much longer time spent at too low a voltage (Situation A pack).
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U think the glued balance wires are unsafe?
Not so much scared of using hot air, just don’t like the method and hoping to find an alternative
Something to consider…
Hot air is how wraps are put on by all the manufacturers. You can use a hair dryer on these PVC wraps, takes only a few seconds each. External cell temp stays under 45°C-50°C if done right.
Otherwise perhaps just use tape or find wraps that are a friction fit and use self-adhesive rings on top? Leaves a gap between the ring and wrap though unless you extend the wrap beyond the cell’s ends.
While highly recommended (unless the risks are fully understood) you don’t need wraps, just insulation between the p-groups and between the pack and the world. Top insulating rings are still mandatory though, of course.
i’m not calling 2.5 heavily discahrged, that’s within spec
but not 12 hours ago you were arguing that you can charge a pack from 1V per cell
2: there was evidence that the battery pack was damaged, and you chose to ignore that and insisted the person to open it up
3: yes
superglue is the far from being an appropriate adhesive to use for balance lead connections
4; and you’re not happy with using a few seconds o fHOT AIR?
that’s like me sayin i’m an absolute GOD in the bed like i’m 50 shades of grey, but i don’t like talking to girls
it makes no sense
Everyone here understands that a broad generalization like “they can be charged” without mentioning the absolutely massive asterisk of the specific conditions that need to be met and the risks associated with doing so is wrong. You dont seem to get that, as you’re still here.
You got there, finally, with that message where you pinged a dozen people, and yet here you are again, saying “they can be charged” without mentioning all the other specific conditions and the risks associated.
And yes, if you’re going to say “you can charge a cell from 1V” it absolutely fucking has to come with that huge disclaimer of an asterisk. Anything else is negligent.
YES.
If youre going to make such a potentially negligent claim, it absolutely has to come with the specific disclaimer of the conditions required and risks associated.
If you dont fucking do that, youre gonna end up with some amateur quoting your forum post a year from now and burning their house down because they tried to slam regular charge current into a 1V cell.
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Frankly I don’t think you have the technical knowledge necessary to give a proper disclaimer.
I don’t think you know how to properly revive a cell from 1v.
I don’t think you should be giving any advice at all about battery building.
I think the only disclaimer that should come with whatever you say is don’t listen to this guy.
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@jamie this is getting out of hand, any chance to clean it up? 2+ days and 200 posts of poop.
It starts here 
There’s some relevant info, but mostly shit.
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