How to revive a dead 18650 (or any) Li-ion battery cell
This is not a permanent way to charge an 18650 cell. The point of this method is just to bring up the voltage of the dead cell to a point that is enough for a real 18650 charger to accept it and charge it properly. When a Li-ion battery does not have high enough voltage, the charger will not charge it. I think the reason is safety because if the voltage is too low, it might take a risk of charging a NiMH or NiCad cell which are only 1.2 volts each. And if you put a NiMH or NiCad cell (at 1.2 Volts) in a Li-ion charger that charges up to 4.2 volts, all hell will break loose.
Also: don't overdischarge the Li-ion cells down to below 3V especially below the threshold recognized by the charger. Otherwise, it will not live long. The “Goldilocks” zone for a long and healthy Li-ion cell life is between 30% and 90% charge. Too much charge or discharge would be bad for the cell.
If you're like me, then you're always looking for an excuse to save money, tinker, or deconstruct something that seems interesting. I found a way to satisfy all of the above! I have an affinity for lithium-ion batteries. They come in all shapes and sizes, are energy-dense (hold a lot of energy), have a higher voltage than NiCad or NiMH batteries, and can withstand high amp draws. Plus, they don't develop a 'memory' or have high self-discharge so you can store them a long time. Lastly, they lend themselves to multicell configurations. Better yet, they're everywhere and can be had for free. In this tutorial, I'll give you a crash-course in how to find, extract, and salvage lithium-ion batteries, so let's get started! Below are the links for some of the tools and items I used!
Like I said, rechargeable lithium-ion batteries are everywhere! This is what makes getting these batteries cheap because people tend to toss old electronics that get broken or just stop working, but leave the battery inside. I usually get mine from the thrift store for pennies, or from old toys people give away or get broken and donate for science. The ones to look for are as follows: hand-held devices, cell phones, digital cameras or camcorders, portable DVD or video players, and my personal favorite, laptop batteries. There are different chemistries associated with rechargeable lithium-ion cells as well such as lithium cobalt oxide (ICR-type), lithium iron phosphate or LiFePO4, (you won't encounter these being thrown away often), lithium manganese oxide (IMR), lithium manganese nickel (INR) and lithium nickle manganese cobalt oxide (NCA or hybrid). The most common you will find are the ICR-type lithium cobalt oxide. It's the best for energy density and power, but has average to low discharge current and temperature threshold. The maximum discharge current for these is equal or at least double the capacity at most. Plus, they are less stable (read: dangerous) than other types and need to have some kind of circuitry protection. Now, let's not confuse lithium-ion batteries with lithium-ion polymer batteries or LiPo batteries. In LiPo batteries the electrolyte, anode, and cathode, positive and negative terminals, are housed in polymer pouches. The internal chemistry is similar to lithium-ion cells. Depending on the device, the battery will be different in shape or size, but they are usually rectangular and thin for cell phones or compact devices, or cylindrical like 18650 (common in laptop batteries) or 18500 common in hump packs for cameras or camcorders.
In case you've ever wondered, the name of the battery contains its dimensions. "18650" means the battery is 18 mm in diameter and 65 mm long. The "0" is just hanging out. Regardless of the type or size, these may have a single cell, or multiple cells. Multiple cells are either in series or parallel, or a mix of both. Even small batteries can have two small cells inside connected in series or series/parallel. This is due to the fact that some devices have increased voltage needs more than a single cell can provide, or to add capacity. Series connections increase the voltage, and parallel connections increase the capacity of the pack. Unlike NiMH or NiCad batteries, lithium-ion battery packs will have some kind of protection device in them like a battery management system consisting of IC's and MOSFET's or resistors that regulate current, voltage, detect short circuits, reverse polarity, and temperature. Some have an added function of balancing the cells if there are multiple cells. Why do they need this? It's because the chemistry of the lithium cell makes it sensitive to over charging, over-discharging (draining until the voltage gets too low), short circuit, and even over temperature. Any of those can damage the cell, or worse, cause a fire. Multiple cell batteries in series need the balance function that makes sure each individual cell receives the same amount of current and voltage as the other cells. If one cell gets more charge than another one, it can be out faster or get damaged. The capacity of the pack is also reduced. These types of batteries also require special charging procedures that NiMH or NiCad's don't. More on that later!
Now before we start digging into battery packs, I want to touch on some safety items specific to lithium-ion cells. If you're into RC and have electric vehicles and have experience with LiPo batteries, you can skip this, but if not, it's important to understand that messing with lithium-ion batteries can be hazardous. I learned this the hard way!
Why? Due to their chemistry, a single 18650 cell holds a lot of energy. Strap 6 or more together, and you have a lot of stored energy. The safety consideration comes if they are short-circuited, over charged, or under charged, or over discharged, the most common type of lithium battery heats up, swells, and can explode, or cause a fire from getting so hot, which we don't 't want.
The way to avoid this is to handle and charge them correctly. Most all lithium-ion battery packs or single batteries have some kind of circuitry protection built into them to protect the cell from being overcharged, short circuited, or over discharged. Multi-cell packs have an added feature called a battery management system with a balance function that monitors and distributes charge current and voltage across each cell, making sure each gets charged with the same amount of current and voltage. That said, you must use an appropriate charger, either for single cells or one that supports multiple cells in a pack such as a balance charger. Using any other charger could cause the lithium-ion cells to overcharge and result in a fire.
Extracting cells is pretty straightforward. You need some basic tools, so here are the essential ones:
Flat blade screwdrivers. It's good to have various sizes, but generally 3 mm (1/8") up to 5 mm (or 1/4") are all you need. Avoid thicker blades as they are too big to fit into small spaces.
Spudger (optional). A sturdy metal one, or strong plastic one for separating cases.
Side cutters or flush cutters. For cutting tabs or wires, or cutting the battery case open. Both work, but I like my flush cutters because they get into small spaces better.
Utility knife. Works better than a spudger, but more dangerous! Ask my fingers and hands how I know this 8)
Multimeter. Don't need a Fluke or anything fancy for this. It's just for measuring the cell voltage to see if they are salvageable.
Gloves (optional). I say optional because practical gloves for this task probably won't stop a sharp screwdriver blade or utility knife blade that's slipped out of a joint at high velocity.
Those are all the tools you need!You have the battery, the tools, and now it's time to dig in. I am taking apart two battery packs in this tutorial. One is a generic 6-cell pack for an HP Pavilion Dv 5 to Dv 6-series laptop and a pack from an ancient (2004 vintage) digital camera rated at 7.4 volts and 1500 mAh. I think it has two cells inside, but we'll find out.
Depending on the type of battery, the basic design is going to be pretty much the same, consisting of a plastic outer casing containing a liner for insulation or cushioning (foam, silastic, tape, or paper), the cell(s), a Protection device/board with its internal connections, either wires, tabs, or wires and tabs. By the way, I've noticed little to no difference in construction between generic (like the laptop battery) and genuine OEM (like the camera battery). Sometimes the case is welded or glued, but other times it's just held together with tabs. You will find out quickly which method the manufacturer uses. OEM batteries are usually glued/welded and cheaper ones are glued or clipped in.
I like to start at the corners of the case with the utility knife first. Find the seam between the two case halves. Inset the knife along the edge. Rock it back and forth to get it going in the case. It should sink in, so be careful not to go too deep and cut the cells or short something out. Once you get it going and have opened up a small gap, time to go for the screwdriver. Use the smaller screwdriver to open the gap further by twisting it. Once you get it opened more, go for the bigger screwdriver and repeat. You should start getting large creases in the case. Move the screw driver up the seam of the case, twisting as you go. If you aren't getting anywhere, go back to the knife and repeat the first step. I don't think I need to remind you to be careful here.
If you're stuck, resist the urge to use a hammer or break out your Dremel tool with a cutoff wheel. If you're like me and impatient, then be super-careful! Batteries don't like being cut open. For the record, I've never had to use mine.
Keep the screwdriver working up the seam and separate the case halves. You can use a sturdy spudger here as a wedge to keep the halves spread open while you work the screwdriver. Be patient! It will give up before you! Don't be afraid to be physical with it. Pry the case apart if needed and dig out the goodies inside.
After some finaggling you should have the case fully or mostly separated and can behold the goodies inside! This is the other fun part, figuring out what you've got inside.
My two batteries happen to have cylindrical cells, but I'll include a flat one so you can see the difference.
The laptop pack has some pretty decent Moli Energy (now called E-One) brand ICR-18650J cells. These are a lesser-known brand that was once located in Canada (now in Taiwan), but are in a variety of devices. I checked the data sheet and they are 2400 mAh capacity and rated at 4000 mA discharge current maximum, 4.2 volts full charge and 3.75 volts nominal charge, and 3 volts discharged. The other pack contains some mysterious cells that are wrapped in plastic coated paper, but I measured them and they come out as 49 mm long and 18 mm wide. I think they are 18500-size lithium-ion cells. The battery case said 1500 mAh for them and 7.4 volts, so there are two cells in series. I would imagine they are good-quality cells since this is an OEM pack, but who knows?
Inside the case we have the same basic features. Both have a battery management board that consists of the protection and balance circuits. The laptop battery adds another important feature, a thermistor to monitor the temperature of the battery. These are designed for maximum capacity and low drain, so you won't find any heavy-duty components like with some other protection circuits.
Taking a look at the arrangement of the batteries, the laptop battery has 6 cells in a series/parallel arrangement, so 3 cells in series to generate the 11.1 volts, and 2 cells in parallel to double the capacity to 4800 mAh. The camera battery has 2 cells in series, so the capacity is the same, but the voltage is doubled.
While it's okay to keep the cells connected, you will want to separate them for charging and analysis. Lithium cells in battery packs are always connected by spot welded tabs that connect the positive and negative terminals and you need to be careful when cutting them. Use the side cutters or the flush cutters to carefully cut the tabs between the cells and avoid shorting across the terminals. Be careful not to damage or remove the protective wrap on the outside of the cell as you can short on the metal body as well while cutting the tabs. We don't want naked batteries. Use the needle nose pliers to remove the tabs by pulling them off. Be careful. The cut edges of the tabs are razor sharp!
Now you have your batteries, was your hard work worth it? The problem with salvaging batteries is you don't know how well they were cared for or how old they are. Lithium-ion batteries are sensitive to over and under-discharging. Any time they are discharged too deeply, then fully charged, they lose capacity. You can check the age of the battery pack, and measure the voltage (if able), or check for date codes on the circuit board inside. Most of the time, these batteries will be dead, and I mean dead. Lithium-ion cells don't like to be discharged below their over discharge voltage, usually between 2.5 and 2.75 volts at the most. Below that and the cell goes to "sleep" or is so dead it won't take a charge anymore, and if you do manage to get charge in it, the capacity will be so low that it's unusable. If you can measure the battery before you take it apart (like our camera battery with exposed terminals), you are looking at 4.2 to 3 volts for a single cell, so our laptop battery fully charged is 12.6 volts and 9 volts discharged. I measured it after I dissected it and it was a pretty-much-dead 5.6 volts with each cell reading around 1.8 volts.
The camera battery is in much better shape, with the pack showing a fully-charged 7.9 volts and each cell at 3.9 volts, but we don't know how healthy they are, or how much of their capacity has been lost over the years.
If your batteries read under 2 volts, then they are "dead." If they read 0 volts, then they have entered a sort of hibernation state and are probably not worth keeping as even if you revive them, they will have been damaged. Recycle them properly. You can salvage the very low voltage cells, but you need a special charger that can 'revive' dead batteries, or use some techniques that can bring them back to life.
You have your batteries, but they're dead. Now what? All is not lost because you can revive them. If you have a balance charger designed for charging LiPo batteries, chances are it will revive your lithium-ion cells too. Or, if you have a digital multicharger that has 'revive' functionality, that will work too. I am using a Chinese clone of a SkyRC iMax B6 charger, and a Zanflare C4 multicharger. The Zanflare has the ability to revive dead batteries and has an analyzer function, but the iMax doesn't.
To use the Zanflare, just insert the dead batteries and let the charger do the work. Always start at the lowest possible charge current. The Zanflare goes down to 300 mAh, so that's fine. It will take a while, but be patient. Let them fully charge, and take them off the charger. Let them sit overnight or a couple days and see if they've lost their charge. If they have significantly self-discharged, then toss 'em, but if they're still holding the charge then chances are you've revived them, but time will tell as you use them whether you are successful. You can run some test cycles on them to see how much life they've lost as well by doing a charge-discharge cycle or two and check the capacity. You can also measure the internal resistance of the cell if your charger has the cell analyzer function, which the Zanflare does. Take this with a grain of salt because lots of variables effect internal resistance, but generally a number around 230 miliohms is a good figure.
If you don't have a Zanflare or other charger/analyzer with revive function, you can use your LiPo charger. Now as a safety feature, most of these chargers will not charge a cell under that 2.6 to 2.5 volt range, but there's a workaround. Just be careful! Charging a lithium-ion cell like a NiMH will cause bad things to happen! Set the charger to the NiMH mode where you can manually select the charge current. Set the current to something like 200 mA and start charging. Monitor the voltage until it gets above 2.8 and stop the charging process. Set the charger to the LiPo/Li-on mode and charge at a low current, like 200 to 300 mA. Let it run until it's fully-charged. Then discharge it at a low setting, 500 mA. Let it discharge fully and note the charged capacity, and the amount of discharged capacity. Charge the cell again and note the charged capacity and you should have a baseline of how much life the cell has in it. A number closer to the original capacity is good, but if your cell discharges rapidly, gets warm or hot, and has low capacity, then it's time to recycle it. The laptop cells were good, averaging around 2400 mAh, spot on their original capacity for all the cells. The camera battery didn't do so well. The cells were badly degraded and their capacity was down to just 550 and 660 mAh fully charged, down from their new 1500 mAh capacity. It makes sense though since this is the original battery from 14 years ago! I will probably use them in another project that's not a high-drain device because these 18500 size cells aren't easy to find.
How to revive a dead 18650 (or any) Li-ion battery cell
This is not a permanent way to charge an 18650 cell. The point of this method is just to bring up the voltage of the dead cell to a point that is enough for a real 18650 charger to accept it and charge it properly. When a Li-ion battery does not have high enough voltage, the charger will not charge it. I think the reason is safety because if the voltage is too low, it might take a risk of charging a NiMH or NiCad cell which are only 1.2 volts each. And if you put a NiMH or NiCad cell (at 1.2 Volts) in a Li-ion charger that charges up to 4.2 volts, all hell will break loose.
Also: don't overdischarge the Li-ion cells down to below 3V especially below the threshold recognized by the charger. Otherwise, it will not live long. The “Goldilocks” zone for a long and healthy Li-ion cell life is between 30% and 90% charge. Too much charge or discharge would be bad for the cell.
If you're like me, then you're always looking for an excuse to save money, tinker, or deconstruct something that seems interesting. I found a way to satisfy all of the above! I have an affinity for lithium-ion batteries. They come in all shapes and sizes, are energy-dense (hold a lot of energy), have a higher voltage than NiCad or NiMH batteries, and can withstand high amp draws. Plus, they don't develop a 'memory' or have high self-discharge so you can store them a long time. Lastly, they lend themselves to multicell configurations. Better yet, they're everywhere and can be had for free. In this tutorial, I'll give you a crash-course in how to find, extract, and salvage lithium-ion batteries, so let's get started! Below are the links for some of the tools and items I used!
Like I said, rechargeable lithium-ion batteries are everywhere! This is what makes getting these batteries cheap because people tend to toss old electronics that get broken or just stop working, but leave the battery inside. I usually get mine from the thrift store for pennies, or from old toys people give away or get broken and donate for science. The ones to look for are as follows: hand-held devices, cell phones, digital cameras or camcorders, portable DVD or video players, and my personal favorite, laptop batteries. There are different chemistries associated with rechargeable lithium-ion cells as well such as lithium cobalt oxide (ICR-type), lithium iron phosphate or LiFePO4, (you won't encounter these being thrown away often), lithium manganese oxide (IMR), lithium manganese nickel (INR) and lithium nickle manganese cobalt oxide (NCA or hybrid). The most common you will find are the ICR-type lithium cobalt oxide. It's the best for energy density and power, but has average to low discharge current and temperature threshold. The maximum discharge current for these is equal or at least double the capacity at most. Plus, they are less stable (read: dangerous) than other types and need to have some kind of circuitry protection. Now, let's not confuse lithium-ion batteries with lithium-ion polymer batteries or LiPo batteries. In LiPo batteries the electrolyte, anode, and cathode, positive and negative terminals, are housed in polymer pouches. The internal chemistry is similar to lithium-ion cells. Depending on the device, the battery will be different in shape or size, but they are usually rectangular and thin for cell phones or compact devices, or cylindrical like 18650 (common in laptop batteries) or 18500 common in hump packs for cameras or camcorders.
In case you've ever wondered, the name of the battery contains its dimensions. "18650" means the battery is 18 mm in diameter and 65 mm long. The "0" is just hanging out. Regardless of the type or size, these may have a single cell, or multiple cells. Multiple cells are either in series or parallel, or a mix of both. Even small batteries can have two small cells inside connected in series or series/parallel. This is due to the fact that some devices have increased voltage needs more than a single cell can provide, or to add capacity. Series connections increase the voltage, and parallel connections increase the capacity of the pack. Unlike NiMH or NiCad batteries, lithium-ion battery packs will have some kind of protection device in them like a battery management system consisting of IC's and MOSFET's or resistors that regulate current, voltage, detect short circuits, reverse polarity, and temperature. Some have an added function of balancing the cells if there are multiple cells. Why do they need this? It's because the chemistry of the lithium cell makes it sensitive to over charging, over-discharging (draining until the voltage gets too low), short circuit, and even over temperature. Any of those can damage the cell, or worse, cause a fire. Multiple cell batteries in series need the balance function that makes sure each individual cell receives the same amount of current and voltage as the other cells. If one cell gets more charge than another one, it can be out faster or get damaged. The capacity of the pack is also reduced. These types of batteries also require special charging procedures that NiMH or NiCad's don't. More on that later!
Now before we start digging into battery packs, I want to touch on some safety items specific to lithium-ion cells. If you're into RC and have electric vehicles and have experience with LiPo batteries, you can skip this, but if not, it's important to understand that messing with lithium-ion batteries can be hazardous. I learned this the hard way!
Why? Due to their chemistry, a single 18650 cell holds a lot of energy. Strap 6 or more together, and you have a lot of stored energy. The safety consideration comes if they are short-circuited, over charged, or under charged, or over discharged, the most common type of lithium battery heats up, swells, and can explode, or cause a fire from getting so hot, which we don't 't want.
The way to avoid this is to handle and charge them correctly. Most all lithium-ion battery packs or single batteries have some kind of circuitry protection built into them to protect the cell from being overcharged, short circuited, or over discharged. Multi-cell packs have an added feature called a battery management system with a balance function that monitors and distributes charge current and voltage across each cell, making sure each gets charged with the same amount of current and voltage. That said, you must use an appropriate charger, either for single cells or one that supports multiple cells in a pack such as a balance charger. Using any other charger could cause the lithium-ion cells to overcharge and result in a fire.
Extracting cells is pretty straightforward. You need some basic tools, so here are the essential ones:
Flat blade screwdrivers. It's good to have various sizes, but generally 3 mm (1/8") up to 5 mm (or 1/4") are all you need. Avoid thicker blades as they are too big to fit into small spaces.
Spudger (optional). A sturdy metal one, or strong plastic one for separating cases.
Side cutters or flush cutters. For cutting tabs or wires, or cutting the battery case open. Both work, but I like my flush cutters because they get into small spaces better.
Utility knife. Works better than a spudger, but more dangerous! Ask my fingers and hands how I know this 8)
Multimeter. Don't need a Fluke or anything fancy for this. It's just for measuring the cell voltage to see if they are salvageable.
Gloves (optional). I say optional because practical gloves for this task probably won't stop a sharp screwdriver blade or utility knife blade that's slipped out of a joint at high velocity.
Those are all the tools you need!You have the battery, the tools, and now it's time to dig in. I am taking apart two battery packs in this tutorial. One is a generic 6-cell pack for an HP Pavilion Dv 5 to Dv 6-series laptop and a pack from an ancient (2004 vintage) digital camera rated at 7.4 volts and 1500 mAh. I think it has two cells inside, but we'll find out.
Depending on the type of battery, the basic design is going to be pretty much the same, consisting of a plastic outer casing containing a liner for insulation or cushioning (foam, silastic, tape, or paper), the cell(s), a Protection device/board with its internal connections, either wires, tabs, or wires and tabs. By the way, I've noticed little to no difference in construction between generic (like the laptop battery) and genuine OEM (like the camera battery). Sometimes the case is welded or glued, but other times it's just held together with tabs. You will find out quickly which method the manufacturer uses. OEM batteries are usually glued/welded and cheaper ones are glued or clipped in.
I like to start at the corners of the case with the utility knife first. Find the seam between the two case halves. Inset the knife along the edge. Rock it back and forth to get it going in the case. It should sink in, so be careful not to go too deep and cut the cells or short something out. Once you get it going and have opened up a small gap, time to go for the screwdriver. Use the smaller screwdriver to open the gap further by twisting it. Once you get it opened more, go for the bigger screwdriver and repeat. You should start getting large creases in the case. Move the screw driver up the seam of the case, twisting as you go. If you aren't getting anywhere, go back to the knife and repeat the first step. I don't think I need to remind you to be careful here.
If you're stuck, resist the urge to use a hammer or break out your Dremel tool with a cutoff wheel. If you're like me and impatient, then be super-careful! Batteries don't like being cut open. For the record, I've never had to use mine.
Keep the screwdriver working up the seam and separate the case halves. You can use a sturdy spudger here as a wedge to keep the halves spread open while you work the screwdriver. Be patient! It will give up before you! Don't be afraid to be physical with it. Pry the case apart if needed and dig out the goodies inside.
After some finaggling you should have the case fully or mostly separated and can behold the goodies inside! This is the other fun part, figuring out what you've got inside.
My two batteries happen to have cylindrical cells, but I'll include a flat one so you can see the difference.
The laptop pack has some pretty decent Moli Energy (now called E-One) brand ICR-18650J cells. These are a lesser-known brand that was once located in Canada (now in Taiwan), but are in a variety of devices. I checked the data sheet and they are 2400 mAh capacity and rated at 4000 mA discharge current maximum, 4.2 volts full charge and 3.75 volts nominal charge, and 3 volts discharged. The other pack contains some mysterious cells that are wrapped in plastic coated paper, but I measured them and they come out as 49 mm long and 18 mm wide. I think they are 18500-size lithium-ion cells. The battery case said 1500 mAh for them and 7.4 volts, so there are two cells in series. I would imagine they are good-quality cells since this is an OEM pack, but who knows?
Inside the case we have the same basic features. Both have a battery management board that consists of the protection and balance circuits. The laptop battery adds another important feature, a thermistor to monitor the temperature of the battery. These are designed for maximum capacity and low drain, so you won't find any heavy-duty components like with some other protection circuits.
Taking a look at the arrangement of the batteries, the laptop battery has 6 cells in a series/parallel arrangement, so 3 cells in series to generate the 11.1 volts, and 2 cells in parallel to double the capacity to 4800 mAh. The camera battery has 2 cells in series, so the capacity is the same, but the voltage is doubled.
While it's okay to keep the cells connected, you will want to separate them for charging and analysis. Lithium cells in battery packs are always connected by spot welded tabs that connect the positive and negative terminals and you need to be careful when cutting them. Use the side cutters or the flush cutters to carefully cut the tabs between the cells and avoid shorting across the terminals. Be careful not to damage or remove the protective wrap on the outside of the cell as you can short on the metal body as well while cutting the tabs. We don't want naked batteries. Use the needle nose pliers to remove the tabs by pulling them off. Be careful. The cut edges of the tabs are razor sharp!
Now you have your batteries, was your hard work worth it? The problem with salvaging batteries is you don't know how well they were cared for or how old they are. Lithium-ion batteries are sensitive to over and under-discharging. Any time they are discharged too deeply, then fully charged, they lose capacity. You can check the age of the battery pack, and measure the voltage (if able), or check for date codes on the circuit board inside. Most of the time, these batteries will be dead, and I mean dead. Lithium-ion cells don't like to be discharged below their over discharge voltage, usually between 2.5 and 2.75 volts at the most. Below that and the cell goes to "sleep" or is so dead it won't take a charge anymore, and if you do manage to get charge in it, the capacity will be so low that it's unusable. If you can measure the battery before you take it apart (like our camera battery with exposed terminals), you are looking at 4.2 to 3 volts for a single cell, so our laptop battery fully charged is 12.6 volts and 9 volts discharged. I measured it after I dissected it and it was a pretty-much-dead 5.6 volts with each cell reading around 1.8 volts.
The camera battery is in much better shape, with the pack showing a fully-charged 7.9 volts and each cell at 3.9 volts, but we don't know how healthy they are, or how much of their capacity has been lost over the years.
If your batteries read under 2 volts, then they are "dead." If they read 0 volts, then they have entered a sort of hibernation state and are probably not worth keeping as even if you revive them, they will have been damaged. Recycle them properly. You can salvage the very low voltage cells, but you need a special charger that can 'revive' dead batteries, or use some techniques that can bring them back to life.
You have your batteries, but they're dead. Now what? All is not lost because you can revive them. If you have a balance charger designed for charging LiPo batteries, chances are it will revive your lithium-ion cells too. Or, if you have a digital multicharger that has 'revive' functionality, that will work too. I am using a Chinese clone of a SkyRC iMax B6 charger, and a Zanflare C4 multicharger. The Zanflare has the ability to revive dead batteries and has an analyzer function, but the iMax doesn't.
To use the Zanflare, just insert the dead batteries and let the charger do the work. Always start at the lowest possible charge current. The Zanflare goes down to 300 mAh, so that's fine. It will take a while, but be patient. Let them fully charge, and take them off the charger. Let them sit overnight or a couple days and see if they've lost their charge. If they have significantly self-discharged, then toss 'em, but if they're still holding the charge then chances are you've revived them, but time will tell as you use them whether you are successful. You can run some test cycles on them to see how much life they've lost as well by doing a charge-discharge cycle or two and check the capacity. You can also measure the internal resistance of the cell if your charger has the cell analyzer function, which the Zanflare does. Take this with a grain of salt because lots of variables effect internal resistance, but generally a number around 230 miliohms is a good figure.
If you don't have a Zanflare or other charger/analyzer with revive function, you can use your LiPo charger. Now as a safety feature, most of these chargers will not charge a cell under that 2.6 to 2.5 volt range, but there's a workaround. Just be careful! Charging a lithium-ion cell like a NiMH will cause bad things to happen! Set the charger to the NiMH mode where you can manually select the charge current. Set the current to something like 200 mA and start charging. Monitor the voltage until it gets above 2.8 and stop the charging process. Set the charger to the LiPo/Li-on mode and charge at a low current, like 200 to 300 mA. Let it run until it's fully-charged. Then discharge it at a low setting, 500 mA. Let it discharge fully and note the charged capacity, and the amount of discharged capacity. Charge the cell again and note the charged capacity and you should have a baseline of how much life the cell has in it. A number closer to the original capacity is good, but if your cell discharges rapidly, gets warm or hot, and has low capacity, then it's time to recycle it. The laptop cells were good, averaging around 2400 mAh, spot on their original capacity for all the cells. The camera battery didn't do so well. The cells were badly degraded and their capacity was down to just 550 and 660 mAh fully charged, down from their new 1500 mAh capacity. It makes sense though since this is the original battery from 14 years ago! I will probably use them in another project that's not a high-drain device because these 18500 size cells aren't easy to find.
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