4 ms·

Although Li-Ion cells are getting cheaper and cheaper every year, it still is worth salvaging the good ones from depleted laptop battery packs. When a laptop ba

Although Li-Ion cells are getting cheaper and cheaper every year, it still is worth salvaging the good ones from depleted laptop battery packs. When a laptop battery pack is gone it's almost always the case of one, max two, 18650 elements that failed, not the whole pack. I've built some good power banks using empty shells (very cheap on Ebay, Aliexpress etc.) and fitting inside the good cells salvaged that way. They last just like new ones once one discards the bad ones. The only caveat is that cells taken from laptop battery packs are not individually protected, that is, they don't employ the small pcb containing a protection against excessive charge, discharge, temperature, short circuit, etc. because the needed circuitry is already contained in the laptop battery pack. Power bank shells do indeed contain such protection, so no problems, but care must be taken into insulating the cells contacts so they cannot short, and before fitting them the user must charge each of them to a known identical voltage, so that once they're put in parallel (remember: no individual protection) the strongest ones won't discharge their energy on weaker ones.

orhmeh09 5y ago
Does this require special knowledge and experience? I would be afraid to try it myself as I suspect that I or my devices would be harmed, either in the process or later on.
- squarefoot 5y ago
  Yes, it does. It's not rocket science, but one must know what he is doing, and as with everything that can become really dangerous, it is better to err on the side of safety. To my knowledge, this is the best informational site around regarding various battery technologies (including Lithium), and how to use them safely. https://batteryuniversity.com/learn/ https://batteryuniversity.com/learn/
quickthrower2 5y ago
Does this come with a “know what you are doing” caveat? I’d be scared of creating an electric firelighter in the process. Also assuming money is no object. Is it as good for the environment to recycle the old battery and buy a refurbed one.
- strbean 5y ago
  I replied with some questions about the safety of this, as I had some concerns when reading it. Aside from the issue I mentioned in reply, the only real caveat would be "know the basics of working with electronics without shorting things or electrocuting yourself" and "check out some youtube videos on rebuilding 18650 packs so you don't do it in a horribly wrong way".
  - Syonyk 5y ago
    > "check out some youtube videos on rebuilding 18650 packs so you don't do it in a horribly wrong way". Bad idea, because about 90% of what they do is fine, and 10% is very, very wrong. Unless you know what you're doing, it's almost impossible to tell which is which.
    - strbean 5y ago
      Fair enough. I haven't seen any of the 10%, but I'm sure they're out there. As an alternative to saying "go find info", how's this: https://www.youtube.com/watch?v=3KDiecphUk8 https://www.youtube.com/watch?v=3KDiecphUk8 ? I just gave it a quick skip through, but the guy seems to know the correct approach.
      - Syonyk 5y ago
        If someone on YouTube is soldering directly to terminals, in any form, they're badly wrong and I wouldn't trust the rest of their judgement. I'm not going to evaluate someone's YouTube video on battery repair, sorry. There's no way I can "skip through it" and have any sense of what they're doing, and I generally try to avoid YouTube as a source of information. You'll find far better material on Endless Sphere, though there are plenty of dangerous ideas there.
- Syonyk 5y ago
  > Does this come with a “know what you are doing” caveat? Yes, and I'll suggest that a disturbingly large fraction of the people doing this on YouTube don't know what they're doing, and are being brutally unsafe with the batteries, even if it works. I've done battery pack rebuilding semi-professionally for a few years (I was rebuilding ebike packs for most of North America from about 2015 to 2018), and the people screwing around with the used/recycled cells scare the hell out of me. In no particular order: * They don't care to invest in a spot welder and they solder directly to the terminals. Every datasheet out there for 18650s that mentions soldering says the same thing: "DO NOT solder directly to our terminals." You spot weld a strip on and then solder to that. Soldering to the terminal puts a ton of heat into the end of the battery which then flows into the cell windings. The separator is usually plastic. You really don't want to weaken it. With a spot welder, I can put my finger on the terminal immediately after spot welding, and I can spread out the welds in time. If I want three welds (six spots) on a terminal, I can do one weld on each cell, then come back for the rest, and keep the temperature "comfortable to a fingertip." I cannot do that soldering. * They tend to take a single snapshot of cell capacity, maybe internal resistance, and then assign cells that way. Unless they organize them by wrapper color for aesthetics, ignoring the cell capacity and behaviors. Some cell chemistries will degrade far faster than others, and you'd ideally like to not have a mess of stuff in the same pack. * They recharge dead cells with no idea how long they've been dead. Lithium cells are physically stressed at full charge and fully empty, and a cell that has been empty for a while may have very real internal physical damage, such that it will fail later. I won't charge anything under 2.5V unless I know exactly how and when it got there, and if it's much below 2.0V, I still won't put voltage to it. The risk of a lithium battery runaway and fire is too high for my tastes. Lithium battery runaways, beyond lighting stuff on fire, tend to emit things like HF, which you very definitely don't want to breathe. It doesn't hurt a bit while it's killing you, because it destroys the nerves first. Health-wise, you're actually better off if the battery venting is flaming, because the mixture of gases coming off that is somewhat less toxic. Again, it depends on the particular chemistry what you get. It's never anything friendly. Unfortunately, "recycling" lithium batteries isn't really established yet, and most of what seems to pass for "recycling" is the cells getting shipped to China, having new ends put on to hide the spot welds, and then getting a shiny wrapper and sold with impossible capacities to vapers for $0.75 or something silly. The highest capacity 18650s are around 3600-3800mAh, and don't source an awful lot of amps in the deal. Anything claiming higher (again, in the 18650 form factor) is certainly a lie. You can do it, if you're careful, but by the time you've properly characterized the batteries, I'm not convinced it's worth the time/effort. Those who claim it is tend to skip a lot of checks and be really, really casual with their packs. To their credit, they rarely catch fire, but the whole "DIY Powerwall" crowd using scavenged and abused cells is not a good example to follow.
strbean 5y ago
I was under the impression that mixing and matching cells (by model or by age/number of charge cycles used) can be sketchy. For example, if you have a very heavily used battery in series with new battery, everything may look okay externally, but you may end up over-discharging the older battery. What are your thoughts on this? Haven't had any issues? Or do you take steps to mitigate it?
- ed25519FUUU 5y ago
  Match them based on internal resistance and capacity after running some tests. Most people don't even really bother with the resistance.
  - Syonyk 5y ago
    You'd be far better off matching them based on percent of original capacity and internal resistance. A 3200mAh cell worn to 2600mAh is in far worse shape than a 2800mAh cell worn to 2600mAh, though you'd probably also see a big difference in internal resistance between them. You might also consider checking IR at various states of charge, if you're being comprehensive. ... and at that point, short of massive automation in a fireproof area, you're almost certainly going to come out ahead buying new cells.
- danhor 5y ago
  Since he mostly talked about having them in parallel, this might not be an issue for him. I also think a bms can solve that issue
  - squarefoot 5y ago
    Yes, I can confirm. I use them only in parallel, and they usually come from the same battery pack. A series connection would require extra care to select them for identical characteristics, and the use of a BMS to keep them balanced, avoiding the strongest ones to discharge at reversed polarity through the weakest ones, which would be a recipe for disasters. BMS circuits however can't do miracles; too different cells shouldn't be used together anyway.
analog31 5y ago
Do you know a good source of info on how to test these cells?
Johnythree 5y ago
Parallel cells will automatically balance as the charged cells feed the discharged cells. There is absolutely no point in trying to balance them.
- sudosysgen 5y ago
  There is. Preventing overcurrent, as the automatic balancing process you are describing can be over hundred times faster than the charging rates the batteries are rated for.
  - squarefoot 5y ago
    You both are right, but there is a caveat: the cells internal resistance. Connecting cells in parallel is inherently safe if done when they're brought all at the same level; from that moment on they won't charge or discharge across each other because the current draw will always bring them at the same voltage, therefore having zero current from cell to cell. The problem is however when one or more cells degrade with age, therefore we have more efficient cells in parallel with less efficient ones. That is not a problem safety wise as well, because as before they'll always be at the same potential, but should their degradation change their internal resistance to a point it's a lot higher than their normal one, then we would have the good cells with lower internal resistance sustaining the most current during charge or discharge, and that could be dangerous. To avoid situations like that one, never implement charges faster than the one that could be sustained by a single cell. Let's say one 2Ah cell can be safely charged at 2C max, that is, 4 Amperes, if we build a pack of 3 of those cells in parallel we would be tempted to charge them at 6C, that is 12 Amperes, which would work in a new pack with all cells that equally balance the current. But if (when) one or two cells degrade their internal chemistry increasing their internal resistance, we'd be left with the remaining good cell(s) drawing the most current, which will largely exceed their individual rating, overheating them and potentially making them explode (that's also when individual cell protection make sense). There's actually a case in which a cell chemistry is so degraded that it can't only store the same amount of current, but also the same voltage, and this could be a problem in parallel packs, but the battery performance drop should have warned us a lot before this happens. So, all we need is to keep the charge current as low as the current sustainable by a single cell, and we're safe. Slow charging also benefits the overall cells life. Don't worry about connecting unprotected cells in parallel, as they balance themselves: all laptop batteries have balanced series of unbalanced parallels. For example, a 6 cell pack contains is arranged as 2p+2p+2p (2 cells in parallel in series with 2 cells in parallel in series with 2 cells in parallel) while 9 cell packs use 3 cells parallels; series cells are balanced through the BMS, but parallel cells will self balance. What is important is to keep series groups balanced and protect against excessive voltage and charge/discharge current.
jandrese 5y ago
The DIY energy storage community is always on the hunt for warehouse sales, closeouts, auctions, etc... on battery packs. There is a cottage industry around buying them up and "shucking" them for the 18650s. It's a lot of work and requires some luck, but you can get hundreds of unused 18650s for like $.50 each.

orhmeh09 5y ago

Does this require special knowledge and experience? I would be afraid to try it myself as I suspect that I or my devices would be harmed, either in the process or later on.

squarefoot 5y ago
Yes, it does. It's not rocket science, but one must know what he is doing, and as with everything that can become really dangerous, it is better to err on the side of safety. To my knowledge, this is the best informational site around regarding various battery technologies (including Lithium), and how to use them safely. https://batteryuniversity.com/learn/ https://batteryuniversity.com/learn/

quickthrower2 5y ago

Does this come with a “know what you are doing” caveat? I’d be scared of creating an electric firelighter in the process. Also assuming money is no object. Is it as good for the environment to recycle the old battery and buy a refurbed one.

strbean 5y ago
I replied with some questions about the safety of this, as I had some concerns when reading it. Aside from the issue I mentioned in reply, the only real caveat would be "know the basics of working with electronics without shorting things or electrocuting yourself" and "check out some youtube videos on rebuilding 18650 packs so you don't do it in a horribly wrong way".
- Syonyk 5y ago
  > "check out some youtube videos on rebuilding 18650 packs so you don't do it in a horribly wrong way". Bad idea, because about 90% of what they do is fine, and 10% is very, very wrong. Unless you know what you're doing, it's almost impossible to tell which is which.
  - strbean 5y ago
    Fair enough. I haven't seen any of the 10%, but I'm sure they're out there. As an alternative to saying "go find info", how's this: https://www.youtube.com/watch?v=3KDiecphUk8 https://www.youtube.com/watch?v=3KDiecphUk8 ? I just gave it a quick skip through, but the guy seems to know the correct approach.
    - Syonyk 5y ago
      If someone on YouTube is soldering directly to terminals, in any form, they're badly wrong and I wouldn't trust the rest of their judgement. I'm not going to evaluate someone's YouTube video on battery repair, sorry. There's no way I can "skip through it" and have any sense of what they're doing, and I generally try to avoid YouTube as a source of information. You'll find far better material on Endless Sphere, though there are plenty of dangerous ideas there.
Syonyk 5y ago
> Does this come with a “know what you are doing” caveat? Yes, and I'll suggest that a disturbingly large fraction of the people doing this on YouTube don't know what they're doing, and are being brutally unsafe with the batteries, even if it works. I've done battery pack rebuilding semi-professionally for a few years (I was rebuilding ebike packs for most of North America from about 2015 to 2018), and the people screwing around with the used/recycled cells scare the hell out of me. In no particular order: * They don't care to invest in a spot welder and they solder directly to the terminals. Every datasheet out there for 18650s that mentions soldering says the same thing: "DO NOT solder directly to our terminals." You spot weld a strip on and then solder to that. Soldering to the terminal puts a ton of heat into the end of the battery which then flows into the cell windings. The separator is usually plastic. You really don't want to weaken it. With a spot welder, I can put my finger on the terminal immediately after spot welding, and I can spread out the welds in time. If I want three welds (six spots) on a terminal, I can do one weld on each cell, then come back for the rest, and keep the temperature "comfortable to a fingertip." I cannot do that soldering. * They tend to take a single snapshot of cell capacity, maybe internal resistance, and then assign cells that way. Unless they organize them by wrapper color for aesthetics, ignoring the cell capacity and behaviors. Some cell chemistries will degrade far faster than others, and you'd ideally like to not have a mess of stuff in the same pack. * They recharge dead cells with no idea how long they've been dead. Lithium cells are physically stressed at full charge and fully empty, and a cell that has been empty for a while may have very real internal physical damage, such that it will fail later. I won't charge anything under 2.5V unless I know exactly how and when it got there, and if it's much below 2.0V, I still won't put voltage to it. The risk of a lithium battery runaway and fire is too high for my tastes. Lithium battery runaways, beyond lighting stuff on fire, tend to emit things like HF, which you very definitely don't want to breathe. It doesn't hurt a bit while it's killing you, because it destroys the nerves first. Health-wise, you're actually better off if the battery venting is flaming, because the mixture of gases coming off that is somewhat less toxic. Again, it depends on the particular chemistry what you get. It's never anything friendly. Unfortunately, "recycling" lithium batteries isn't really established yet, and most of what seems to pass for "recycling" is the cells getting shipped to China, having new ends put on to hide the spot welds, and then getting a shiny wrapper and sold with impossible capacities to vapers for $0.75 or something silly. The highest capacity 18650s are around 3600-3800mAh, and don't source an awful lot of amps in the deal. Anything claiming higher (again, in the 18650 form factor) is certainly a lie. You can do it, if you're careful, but by the time you've properly characterized the batteries, I'm not convinced it's worth the time/effort. Those who claim it is tend to skip a lot of checks and be really, really casual with their packs. To their credit, they rarely catch fire, but the whole "DIY Powerwall" crowd using scavenged and abused cells is not a good example to follow.

strbean 5y ago

I was under the impression that mixing and matching cells (by model or by age/number of charge cycles used) can be sketchy. For example, if you have a very heavily used battery in series with new battery, everything may look okay externally, but you may end up over-discharging the older battery. What are your thoughts on this? Haven't had any issues? Or do you take steps to mitigate it?

ed25519FUUU 5y ago
Match them based on internal resistance and capacity after running some tests. Most people don't even really bother with the resistance.
- Syonyk 5y ago
  You'd be far better off matching them based on percent of original capacity and internal resistance. A 3200mAh cell worn to 2600mAh is in far worse shape than a 2800mAh cell worn to 2600mAh, though you'd probably also see a big difference in internal resistance between them. You might also consider checking IR at various states of charge, if you're being comprehensive. ... and at that point, short of massive automation in a fireproof area, you're almost certainly going to come out ahead buying new cells.
danhor 5y ago
Since he mostly talked about having them in parallel, this might not be an issue for him. I also think a bms can solve that issue
- squarefoot 5y ago
  Yes, I can confirm. I use them only in parallel, and they usually come from the same battery pack. A series connection would require extra care to select them for identical characteristics, and the use of a BMS to keep them balanced, avoiding the strongest ones to discharge at reversed polarity through the weakest ones, which would be a recipe for disasters. BMS circuits however can't do miracles; too different cells shouldn't be used together anyway.

analog31 5y ago

Do you know a good source of info on how to test these cells?

Johnythree 5y ago

Parallel cells will automatically balance as the charged cells feed the discharged cells. There is absolutely no point in trying to balance them.

sudosysgen 5y ago
There is. Preventing overcurrent, as the automatic balancing process you are describing can be over hundred times faster than the charging rates the batteries are rated for.
- squarefoot 5y ago
  You both are right, but there is a caveat: the cells internal resistance. Connecting cells in parallel is inherently safe if done when they're brought all at the same level; from that moment on they won't charge or discharge across each other because the current draw will always bring them at the same voltage, therefore having zero current from cell to cell. The problem is however when one or more cells degrade with age, therefore we have more efficient cells in parallel with less efficient ones. That is not a problem safety wise as well, because as before they'll always be at the same potential, but should their degradation change their internal resistance to a point it's a lot higher than their normal one, then we would have the good cells with lower internal resistance sustaining the most current during charge or discharge, and that could be dangerous. To avoid situations like that one, never implement charges faster than the one that could be sustained by a single cell. Let's say one 2Ah cell can be safely charged at 2C max, that is, 4 Amperes, if we build a pack of 3 of those cells in parallel we would be tempted to charge them at 6C, that is 12 Amperes, which would work in a new pack with all cells that equally balance the current. But if (when) one or two cells degrade their internal chemistry increasing their internal resistance, we'd be left with the remaining good cell(s) drawing the most current, which will largely exceed their individual rating, overheating them and potentially making them explode (that's also when individual cell protection make sense). There's actually a case in which a cell chemistry is so degraded that it can't only store the same amount of current, but also the same voltage, and this could be a problem in parallel packs, but the battery performance drop should have warned us a lot before this happens. So, all we need is to keep the charge current as low as the current sustainable by a single cell, and we're safe. Slow charging also benefits the overall cells life. Don't worry about connecting unprotected cells in parallel, as they balance themselves: all laptop batteries have balanced series of unbalanced parallels. For example, a 6 cell pack contains is arranged as 2p+2p+2p (2 cells in parallel in series with 2 cells in parallel in series with 2 cells in parallel) while 9 cell packs use 3 cells parallels; series cells are balanced through the BMS, but parallel cells will self balance. What is important is to keep series groups balanced and protect against excessive voltage and charge/discharge current.

jandrese 5y ago

The DIY energy storage community is always on the hunt for warehouse sales, closeouts, auctions, etc... on battery packs. There is a cottage industry around buying them up and "shucking" them for the 18650s. It's a lot of work and requires some luck, but you can get hundreds of unused 18650s for like $.50 each.