I literally just revived a dead 18650 (showing tens of millivolts) by using the nicad function. Long story but I tried soldering my battery bank at first and decided half way to abort and use a spot welder. Removing the solder proved stressful and I had 3 cells dive on me, (out of 238 cells, not a bad fall out rate). We might be tip toeing on being battery doctors by how complex things seem to get with even a simple 5 minute diy video. Thanks a bunch for the tips. Great video.
Have discovered an easy way to do this. I put a couple of good cells in my liito kala and a dead one I disconnect power. in a couple of minutes, I reconnect power charge the dead cell then test the capacity. I am no genius but I thought this through and it worked for me.
I have two that just sit dead when using the bench top at 4v at any milli-amp, or my Hi-tec x1 rc charger I disassembled two laptop battery packs that had sat for a long time so all cells were very low, I just wanted to weed out the bad apples, thank you.
1) Can you do a review on charge controllers and why you choose the one your using? 2) how can you get inverters to only come on after sunset, shut off at sunrise?
1. Sure could. Dont have enough different types to look at neither enough info perhaps but some day. 2. Why do you want it on after sunset? It can be done either with a time controlled switch or a lightning sensitive switch.
Thanks, you saved my ecig 18650s! I used the NiMh method at 0.12A. And 3 or 4 bumps each brought them back from 0.7V!!! That got them JUST above 2V, where I quickly "caught" them and the Li-Io charge started... 2.714V and climbing now! Is it normal the charge starts slow? Set it at 2A, but it's going at 0.15... I assume it will pick up once the Voltage approaches more "normal" levels?
I have revived these batteries several times. But sometimes nothing helps. Even revived batteries sometimes have only 30% capacity. Sometimes 100%. It's a lottery, but it's worth a try!
good video, early in computers I remember something about pcb's in computers, so I looked it up looks like there's 2 meanings, pcb's(organic) released when a capacitor heats up more than room temperature and printed circuit boards. The nickle rechargeable if they were more weatherprotected they would be better, if the nickle rechargeable heats up more than room temperature and releases fumes would it be pcb's as well?
I'm here from eevblog how to charge a li-ion with a power supply, How did I ever live before my bench top power supply. Thanks for the info, Are you in Germany?
you can use the imax b6 to bump charge/revive your dead or low voltage 18650 cells........ lithium charging.. then set the settings to the desired charging current.. and change the settings from 1s to auto... and it will charge it...
You can actually do it with Imax B6 by cheating a bit. First charge cell up to 1.2V with NiCd/NiMH program. Then charge up to 2.4 V with Pb (lead acid) battery program. Then charge up 3.4V using the LiFePO4 program. Then charge up to 4.20V using the LiPo program. There you go. Charge at very low amperage (0.1A) up to at least 2.5V.
I just charge 0v batteries using a tp4056 or cheap powebank case from alliexpres and the cell gets charge enough without problem. After that I finish the process with opus.
Great tutorial, smart solution by using another cell to charge the low voltage one. Note: you meantioned it's possible to use more resistors for spreading the load on them, yes it's possible but there is a note to it. When you connect them in serie you will need to divide the total calculated value (in series it will add the values of the resistors) and with parallel you need to double it (parallel will divide the value by 2 if there are 2 resistors with the same value parallel). If you need to buy just buy one with a higher wattage.
Thanks. The 2x resistors or so is more if you got 1/4th or 1/8th W resistors you can still use those as long as you use a couple more of them :) For instance 2x 160Ohm in paralell is 80Ohm and will then spread the load :) Eya you get it :)
Hello, Could you please inform if my battery is defective? I have an 18650 battery at no load measures 4.2v but under load it drops to 2.5v. The battery will not take a charge via my XTAR VC2 charger because the charger sees the battery at voltage capacity, i.e. full. When I connect the battery to an external power supply set at 4v and a constant current of 100mA, the current reading stays at 0. Is this battery defective? Thank you very much for all your help and great video tutorials.
@@DIYTechRepairs any reason why I can't put two batteries in series, say they're both at 1v each, to fool the charger into thinking it's a single battery at 2v and get the charge started? How does battery resistance affect the charging?
@@areyouavinalaff You can but at same time you need to monitor so not one of them jumps to high and the other stays flat. Its better just to do it properly :)
I've been waiting to find an answer whether or not lithium could be charged in parallel or series. A dead nonrechargable nickel will charge like an electrolytic on a lithium charger it'll take some juice once it reads full take it out and try it, this means one could refill a nickel nonrechargable if it had a port, I'm not going to try the reverse, filling an electrolytic.
so if the nonrechargable nickel reaches full charge off a lithium charger acting like an electrolytic just like an overcharged electrolytic it could blow up right? maybe you could take a dead nickle nonrechargable and use it in place of a electrolytic might hold more capacity.
I have 2000watts of solar grid tie, 4000 watts hooked to a lead acid battery tied into a Outback hybrid inverter. I am installing another 6000 watts that is going to my li-ion powerwall that, 3000 watts of that goes to my Outback 24volt inverter the other 3000 watts going to my Outback 48volt inverter. I would like to use my powerwall for our house's nighttime power use. My powerwall will be over 40kw when I'm done. Hopefully 60 kw. I'm at 49 degrees latitude, so like you, I need a lot of back up in the winter! Hopefully you can give me some suggestions?
If you have a hybrid inverter that one will do what you want for you in terms of using battery when not enough solar exist. You should be able to set in that inverter what order you should use as source. Ie Solar > Battery > grid. For the normal inverters always draw power from the battery and that will work out on its own.
I have a quick question. I have a 10s2p battery that have the volt drop to 18.53. just wondering if I can bump up the voltage using the DC power supply method, maybe can advice what voltage I should start with and how much current to start with... Many thanks
Yes you can. Best is though ro bump each cell Group Up to 3v and then max 100mA per cell. Then when all 10 groups are done you're back in business. Bmping overall voltage is a bit riskier and you then need to monitor each cells voltgae
@@DIYTechRepairs it comes as a pack... Bumping each one means I would have to rip open the pack... If am to bump the pack... What is the suggested voltage though
@@stanleytan9717 You dont have access to the balance wires? If you dont have that you can only guess that it will work and that the internal BMS will do its job if one cell fails. Overall total voltage would be 30+ volt if its 10s.
@@DIYTechRepairs Thank you for your reply. I did measure resistance on thr positive side of the bumper (with resistor) It gives me 82ohm. The other side (negative) gives 0 ohm. When I put two batteries in parallel mode( one is 4.2v another in 1.7v) It charges battery, but it happens too fast. When I measure current flowing on 1.7v I get around 500mA. I understand your math is right, I am just puzzled what could I be doing wrong. Maybe faulty resistor? It seems to be slowly dropping though. It dropped to 100mA. Theres is a possibility that it can't be measured properly while it is charging with the tools I have. Ok, finaly, I figured it out. If I have only one charged battery in the bumper (4.2v) in slot 1, and slot 2 is empty, it measures 50mA on the slot 2 leads. I guess it was drawing current from second battery as well, when I was measuring it first time.
Really nice! Man, I opened a notebook battery one and all batteries had 0.6v. All of them. So I charged them using a TP4056 connected to a 18650 holder. Then, when I finally got a battery tester and tested them... Surprise: values between 2100 and 2200mAh. Still have them and didn't used yet. I'm going to make a huge power bank. :D
hehe good on you. I'm still looking for laptop repair places willing to help. Some I called and they say they're busy and email them, so I did.. no response.. grr I think you'll need to cycle those cells a few times and see how well they work, probably just flattened the shit out of it and wasn't due to a problem causing them to go so low. hopefully if you charged them slowly, it wouldn't have damaged them internally, at least if not already from the 0.6v
Phizicks Yeah, but they are more than good, probably only the BMS stopped working. :) Anyway, I use to buy notebook batteries in a "exchange fair" (at least is how we call here in Brazil). You know? It's a fair where people sell new and used things, farm animals, even sell or give pets, and a lot of people sell parts of old and broken tools, DVDs and so on. It happens once a week, every Sunday. I already bought a lot of good stuff there, like dc motors and so on, that I use in my projects/videos. :)
Any help for my 18650 i've done this method but nothing i overcharged it i was supposed to charge it half an hour but i charged it for 2 hours shit i need help with this. I sleep for 2 hours i forgot i was charging it
@@DIYTechRepairs hehehe guess i wont be messing with it any more i threw it away when i heard a hissing when i push it down with a very verryyy small pressure to it it scared me and also there was a fluid coming out of it. It does smell like acetone there is no way im messing the other battery btw thanks for this vid. And this method really does work but be very careful when doing this cause my battery was really soft when i push on its disc or something
My battery is 36v... I don't have a fancy charger.. But I have another 36v (10S1P) ... Can I hook them together with a resistor? 50mA seems super low.. I'd rather do 300-500mA like a normal charger... If urs 0.21w for 1 cell.. Can I use that x10 so 2.1w for 50mA. Then 21w for 500mA?
Hi need some help on these 18650. I’m new to these type of batteries and a little bit nervous on charging them. Do I need a multimeter to check if the voltage is above 2v or can I just put it in the charger as normal, bit confused on what to do. Link below on the batteries I bought. Sorry for being a noob. www.ebay.co.uk/itm/4-x-UltraFire-18650-8800mAh-3-7V-Li-ion-Rechargeable-3-PIN-UK-Battery-Charger/262425807293?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649
First of all bin those cells. They are FAKE... You should have watched my video about fake cells :) But yes when you get real cells just put them in the charger
I have 6 18650 cells which I took off from from a laptop battery that was loosing it's charge in just 15 to 30 minutes. I took off the cells from the casing they were dead I did CID and the voltage increased to 3.7 to 4.2 v in each cell . I used it for my rc plane when I gave full throttle the voltage of battery decreased from 11.7 to 4.5 volt and after sometime it again came to 11.1volt .whenever I give load on these batteries their voltage decrease and gradually increase when there is no load .Please help
All cells taking charge is worth testing. I would say that many below 2V is not comming back good enough for my liking. But this depends on why they are on low voltage from the start. I test em all
Or you could get a proper charger like an nitecore charger or a XTar charger folks I wouldn't recomend that you charge your batteries like the Dude in this video did
You can but bumping a cell with resistor is as fine and easier than running above chargers in NiMh mode to get the voltage up. I would rather use a proper Bench PSU than above chargers to do that if so ;)
The resistance of a new cell is in the 10s of milliohms, orders of magnitude less than the current-limiting resistor. A damaged cell will only have a higher internal resistance, limiting the current even more.
I kind of only went with the worst case scenario and made the calculation very very simple. There is much to be added there in you want the exact current flowing but for our use case i left that out. :)
To clarify point number one: the possible internal resistances of the cells is so small that it is masked by the manufacturing uncertainty of ... well, any physical resistor you could possibly attempt to produce economically. Your 1% 1k resistor don't give a crap about your puny 170 mOhm hissy-fit of worst-case-scenario.
The internal resistance is only interesting for the (dis)charge properties of the battery. When the value is to high you will experience a larger voltage drop at higher currents. The value of the internal resistance is in this application to small to limit the current, but it can create a problem with the voltage drop. For example that the battery can't be charged full at a higher current or that the the voltage drops to fast. Both situations can create an instability in the pack. AveRage Joe has videos about testing fuse wire where he explains why, if a cell is not equal to the others in the pack it can cause a current draw. Something you don't want to happen.
You obviously know your stuff, I really appreciate the time you put into making these videos- thank you.
I literally just revived a dead 18650 (showing tens of millivolts) by using the nicad function. Long story but I tried soldering my battery bank at first and decided half way to abort and use a spot welder. Removing the solder proved stressful and I had 3 cells dive on me, (out of 238 cells, not a bad fall out rate). We might be tip toeing on being battery doctors by how complex things seem to get with even a simple 5 minute diy video. Thanks a bunch for the tips. Great video.
Very good and good safety advice at the end, ie do not use or trust a cell which has been damaged or over pressurised before
Wow comprehensively explained! I've seen people drilling the positive terminal without exolaining why the need to ... Awesome work!
Thank you! I successfully revived a few batteries using the NiMH charging method before being able to use the LiPo charging. Very happy!! :D
Hi how long did you bump them for?
Excellent. Thank you for posting this informative video, I would never have thought to use NiMH mode.
Hi Daromer. Another top video for my favorites list, very informative as always.
Keep up the good work.
Thomas K. au.
Have discovered an easy way to do this. I put a couple of good cells in my liito kala and a dead one I disconnect power. in a couple of minutes, I reconnect power charge the dead cell then test the capacity. I am no genius but I thought this through and it worked for me.
Cool
This worked for me as well! Thank you, It takes about an hour to go from 1.7v to 2.2v. Then charger can do normal charging.
This guy knows what he is talking about.
I wonder why only 2 cells where not charging 👍 great video 🤖
many many thanks for this tutorial WITH GREAT EXPLANATIONS !!! DANKE DANKE DANKE
By the way, thanks for your very informative videos, always enjoy them.
Thanks, i have a cell with 0.5 volts, i appreciate the information 👍🏻
Awesome video. Thank you. Just confirming an 82 ohm resistor
Thanks a lot for this video
Great video.
OMG I love you for this!!!!!manual nimh charging ftw
I have two that just sit dead when using the bench top at 4v at any milli-amp, or my Hi-tec x1 rc charger
I disassembled two laptop battery packs that had sat for a long time so all cells were very low,
I just wanted to weed out the bad apples, thank you.
Thank you!
many thanks ... greet explanation keep posting
Top from Brasil friend
1) Can you do a review on charge controllers and why you choose the one your using? 2) how can you get inverters to only come on after sunset, shut off at sunrise?
1. Sure could. Dont have enough different types to look at neither enough info perhaps but some day.
2. Why do you want it on after sunset? It can be done either with a time controlled switch or a lightning sensitive switch.
Just use the nimh setting on imax- watch them until they are around 2.8- then switch to lipo.
good job thank you
Thank you so much sir.! Amazing video, big help for us. Saves money, very informative DIY ! 😊👍
Great video and explanation.
Thanks, you saved my ecig 18650s! I used the NiMh method at 0.12A. And 3 or 4 bumps each brought them back from 0.7V!!! That got them JUST above 2V, where I quickly "caught" them and the Li-Io charge started... 2.714V and climbing now! Is it normal the charge starts slow? Set it at 2A, but it's going at 0.15... I assume it will pick up once the Voltage approaches more "normal" levels?
My jaw drop when the voltage back to 3volt after you push it down a little bit
same happened to me was at like 2volts and jumped back up to 3.2v
@@Gamer-nc8qp mine got 0.7 v then after i push like in the video it back to 3.8 v.. wth is that!!!
Very good.
Awesome video! Keep up the great work mate!!
I have revived these batteries several times. But sometimes nothing
helps. Even revived batteries sometimes have only 30% capacity.
Sometimes 100%. It's a lottery, but it's worth a try!
Thanks! interesting.
good video, early in computers I remember something about pcb's in computers, so I looked it up looks like there's 2 meanings, pcb's(organic) released when a capacitor heats up more than room temperature and printed circuit boards. The nickle rechargeable if they were more weatherprotected they would be better, if the nickle rechargeable heats up more than room temperature and releases fumes would it be pcb's as well?
Very instructive! Thanks!
Damn, your videos are really informative!
I'm here from eevblog how to charge a li-ion with a power supply,
How did I ever live before my bench top power supply.
Thanks for the info, Are you in Germany?
Sweden so Close :)
you can use the imax b6 to bump charge/revive your dead or low voltage 18650 cells........ lithium charging.. then set the settings to the desired charging current.. and change the settings from 1s to auto... and it will charge it...
thanks it was very useful.
can you revive 18650 safely with powerbank
You can actually do it with Imax B6 by cheating a bit. First charge cell up to 1.2V with NiCd/NiMH program. Then charge up to 2.4 V with Pb (lead acid) battery program. Then charge up 3.4V using the LiFePO4 program. Then charge up to 4.20V using the LiPo program. There you go. Charge at very low amperage (0.1A) up to at least 2.5V.
Interesting
Nice work, thank you for this video :)
Thank you too!
Can you do this without a resistor? I’m burning shit and making sparks. So sad I just got a new laser and can’t use it
What do I do ??????I have some batteries with 4.2 vols but no capacity whatsoever and they would not charge.
You recycle Them. They have their cid triggered = crap
Need video charging low voltage 18650 with IMAX b6
Finally found someone who speak English
I just charge 0v batteries using a tp4056 or cheap powebank case from alliexpres and the cell gets charge enough without problem. After that I finish the process with opus.
Great information as always. Auf Wiedersehen:)
Great tutorial, smart solution by using another cell to charge the low voltage one. Note: you meantioned it's possible to use more resistors for spreading the load on them, yes it's possible but there is a note to it. When you connect them in serie you will need to divide the total calculated value (in series it will add the values of the resistors) and with parallel you need to double it (parallel will divide the value by 2 if there are 2 resistors with the same value parallel). If you need to buy just buy one with a higher wattage.
Thanks. The 2x resistors or so is more if you got 1/4th or 1/8th W resistors you can still use those as long as you use a couple more of them :) For instance 2x 160Ohm in paralell is 80Ohm and will then spread the load :) Eya you get it :)
This is not difficult for me, learned this on school. 😉
Hello,
Could you please inform if my battery is defective? I have an 18650 battery at no load measures 4.2v but under load it drops to 2.5v. The battery will not take a charge via my XTAR VC2 charger because the charger sees the battery at voltage capacity, i.e. full. When I connect the battery to an external power supply set at 4v and a constant current of 100mA, the current reading stays at 0. Is this battery defective?
Thank you very much for all your help and great video tutorials.
The CID is most likely triggered or the cell is just very bad. I would recycle the battery and get a new one instead.
@@DIYTechRepairs OK, thank you very much for the very quick reply.
What's the lowest voltage a charger requires to detect a 18650?
Depends on Charger. But 1.5v+
@@DIYTechRepairs any reason why I can't put two batteries in series, say they're both at 1v each, to fool the charger into thinking it's a single battery at 2v and get the charge started? How does battery resistance affect the charging?
@@areyouavinalaff You can but at same time you need to monitor so not one of them jumps to high and the other stays flat. Its better just to do it properly :)
I've been waiting to find an answer whether or not lithium could be charged in parallel or series. A dead nonrechargable nickel will charge like an electrolytic on a lithium charger it'll take some juice once it reads full take it out and try it, this means one could refill a nickel nonrechargable if it had a port, I'm not going to try the reverse, filling an electrolytic.
so if the nonrechargable nickel reaches full charge off a lithium charger acting like an electrolytic just like an overcharged electrolytic it could blow up right? maybe you could take a dead nickle nonrechargable and use it in place of a electrolytic might hold more capacity.
I've managed to charge my battery on imax by just staying on LiIo program and keeping the voltage setting on auto
I have 2000watts of solar grid tie, 4000 watts hooked to a lead acid battery tied into a Outback hybrid inverter. I am installing another 6000 watts that is going to my li-ion powerwall that, 3000 watts of that goes to my Outback 24volt inverter the other 3000 watts going to my Outback 48volt inverter. I would like to use my powerwall for our house's nighttime power use. My powerwall will be over 40kw when I'm done. Hopefully 60 kw. I'm at 49 degrees latitude, so like you, I need a lot of back up in the winter! Hopefully you can give me some suggestions?
If you have a hybrid inverter that one will do what you want for you in terms of using battery when not enough solar exist. You should be able to set in that inverter what order you should use as source. Ie Solar > Battery > grid. For the normal inverters always draw power from the battery and that will work out on its own.
biltema perkele
I have a quick question. I have a 10s2p battery that have the volt drop to 18.53. just wondering if I can bump up the voltage using the DC power supply method, maybe can advice what voltage I should start with and how much current to start with...
Many thanks
Yes you can. Best is though ro bump each cell Group Up to 3v and then max 100mA per cell. Then when all 10 groups are done you're back in business. Bmping overall voltage is a bit riskier and you then need to monitor each cells voltgae
@@DIYTechRepairs it comes as a pack... Bumping each one means I would have to rip open the pack... If am to bump the pack... What is the suggested voltage though
@@stanleytan9717 You dont have access to the balance wires? If you dont have that you can only guess that it will work and that the internal BMS will do its job if one cell fails. Overall total voltage would be 30+ volt if its 10s.
@@DIYTechRepairs thank you very much for the information and really appreciate the help and quick response even though this video is out for so long!
82ohm for max 50mA current. After assembling battery bumper. I get around 500ma flow. Did I do something wrong?
U = I * R. If you get 500mA you have a resistor of = 4,2/0,5 = 8,4Ohm and not 82 ohm...
@@DIYTechRepairs Thank you for your reply. I did measure resistance on thr positive side of the bumper (with resistor) It gives me 82ohm. The other side (negative) gives 0 ohm. When I put two batteries in parallel mode( one is 4.2v another in 1.7v) It charges battery, but it happens too fast. When I measure current flowing on 1.7v I get around 500mA. I understand your math is right, I am just puzzled what could I be doing wrong. Maybe faulty resistor? It seems to be slowly dropping though. It dropped to 100mA. Theres is a possibility that it can't be measured properly while it is charging with the tools I have.
Ok, finaly, I figured it out. If I have only one charged battery in the bumper (4.2v) in slot 1, and slot 2 is empty, it measures 50mA on the slot 2 leads. I guess it was drawing current from second battery as well, when I was measuring it first time.
Super
Really nice! Man, I opened a notebook battery one and all batteries had 0.6v. All of them. So I charged them using a TP4056 connected to a 18650 holder. Then, when I finally got a battery tester and tested them... Surprise: values between 2100 and 2200mAh. Still have them and didn't used yet. I'm going to make a huge power bank. :D
hehe good on you. I'm still looking for laptop repair places willing to help. Some I called and they say they're busy and email them, so I did.. no response.. grr
I think you'll need to cycle those cells a few times and see how well they work, probably just flattened the shit out of it and wasn't due to a problem causing them to go so low. hopefully if you charged them slowly, it wouldn't have damaged them internally, at least if not already from the 0.6v
Phizicks Yeah, but they are more than good, probably only the BMS stopped working. :) Anyway, I use to buy notebook batteries in a "exchange fair" (at least is how we call here in Brazil). You know? It's a fair where people sell new and used things, farm animals, even sell or give pets, and a lot of people sell parts of old and broken tools, DVDs and so on. It happens once a week, every Sunday. I already bought a lot of good stuff there, like dc motors and so on, that I use in my projects/videos. :)
Any help for my 18650 i've done this method but nothing i overcharged it i was supposed to charge it half an hour but i charged it for 2 hours shit i need help with this.
I sleep for 2 hours i forgot i was charging it
No problem if voltage was det below 4.2
@@DIYTechRepairs hehehe guess i wont be messing with it any more i threw it away when i heard a hissing when i push it down with a very verryyy small pressure to it it scared me and also there was a fluid coming out of it. It does smell like acetone there is no way im messing the other battery btw thanks for this vid. And this method really does work but be very careful when doing this cause my battery was really soft when i push on its disc or something
Alltså ja fattar inte va ni har alla batterier till? Varför alla batterier? Mvh/ nick
Nicklas Olsson för att driva elen i huset
DIY Tech & Repairs, ok 👍 riktigt intressant faktiskt.
what about 0v cells, they are shorted
Can be yes but dont have to.
My battery is 36v... I don't have a fancy charger.. But I have another 36v (10S1P) ... Can I hook them together with a resistor? 50mA seems super low.. I'd rather do 300-500mA like a normal charger...
If urs 0.21w for 1 cell.. Can I use that x10 so 2.1w for 50mA. Then 21w for 500mA?
Im not sure what you want to do? No you should not hook 2 in parallell like that unless they have proper bms atached
Hi need some help on these 18650. I’m new to these type of batteries and a little bit nervous on charging them.
Do I need a multimeter to check if the voltage is above 2v or can I just put it in the charger as normal, bit
confused on what to do. Link below on the batteries I bought. Sorry for being a noob. www.ebay.co.uk/itm/4-x-UltraFire-18650-8800mAh-3-7V-Li-ion-Rechargeable-3-PIN-UK-Battery-Charger/262425807293?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649
First of all bin those cells. They are FAKE... You should have watched my video about fake cells :) But yes when you get real cells just put them in the charger
I have 6 18650 cells which I took off from from a laptop battery that was loosing it's charge in just 15 to 30 minutes. I took off the cells from the casing they were dead I did CID and the voltage increased to 3.7 to 4.2 v in each cell . I used it for my rc plane when I gave full throttle the voltage of battery decreased from 11.7 to 4.5 volt and after sometime it again came to 11.1volt .whenever I give load on these batteries their voltage decrease and gradually increase when there is no load .Please help
there's a minimum voltage for the cell to bring them back to life, and in your experience one the cell is back how good the cell is going to be
All cells taking charge is worth testing. I would say that many below 2V is not comming back good enough for my liking. But this depends on why they are on low voltage from the start. I test em all
Just dont do it.
Or you could get a proper charger like an nitecore charger or a XTar charger folks
I wouldn't recomend that you charge your batteries like the Dude in this video did
You can but bumping a cell with resistor is as fine and easier than running above chargers in NiMh mode to get the voltage up. I would rather use a proper Bench PSU than above chargers to do that if so ;)
No useful video. How many people have your kind of equipment?
Did you think you just can wave a Magic wand?
Regarding the parallel charging of cells calculation. Don't you need to consider the resistance of the dead cell???
The resistance of a new cell is in the 10s of milliohms, orders of magnitude less than the current-limiting resistor. A damaged cell will only have a higher internal resistance, limiting the current even more.
I kind of only went with the worst case scenario and made the calculation very very simple. There is much to be added there in you want the exact current flowing but for our use case i left that out. :)
To clarify point number one: the possible internal resistances of the cells is so small that it is masked by the manufacturing uncertainty of ... well, any physical resistor you could possibly attempt to produce economically.
Your 1% 1k resistor don't give a crap about your puny 170 mOhm hissy-fit of worst-case-scenario.
The internal resistance is only interesting for the (dis)charge properties of the battery. When the value is to high you will experience a larger voltage drop at higher currents. The value of the internal resistance is in this application to small to limit the current, but it can create a problem with the voltage drop. For example that the battery can't be charged full at a higher current or that the the voltage drops to fast. Both situations can create an instability in the pack. AveRage Joe has videos about testing fuse wire where he explains why, if a cell is not equal to the others in the pack it can cause a current draw. Something you don't want to happen.