Here at Hackerfarm, we use 18650 rechargeable lithium ion batteries for just about everything. We also hate throwing out rechargeable batteries if we can avoid it. Recently we were going through our lithium-ion battery stock and found out that a bunch of them were completely discharged and could not be revived. The battery chargers we connected them to were not charging at all. For lithium-ion batteries, the fully charged cell is around 4.2V and a discharged cell is around 3.0V. A deeply discharged cell has fallen below 2.5V and most lithium-ion battery chargers can’t revive cells that have discharged this deeply.
Once a battery reaches below 2.5V, the low voltage cutoff threshold, it goes into a sleep mode where the protection circuit shuts down all operations. Most battery chargers won’t charge a battery below 2.5V which means the battery you have is essentially useless. What you have to do is provide enough charge to the battery to boost the voltage above the low voltage cutoff threshold. Once this happens, the protection circuit kicks in and the battery can be charged normally. This is also a great way to salvage 18650’s, especially from dead laptop computer battery packs.
Some chargers have a “boost” feature to charge a deeply discharged battery and revive it but there’s actually an easy way to do it. You just connect the battery to a voltage source (3.5~5.0V) and charge it for around 5 minutes to get the voltage up. Once that happens, you can put the battery inside a charger and get it to charge normally. One caveat is that you should be present when you do this the whole time. You don’t want to leave the battery connected to an unsupervised 5V source since it could overcharge and cause a fire. Also, you’ll want to supervise the charging of the batteries inside the charger to make sure they are okay and don’t heat up or inflate (outgas).
Here you can see me reviving some dead 18650 batteries that have been in storage for too long. This particular battery is at 0.423V which is way below the 2.5V cutoff. It cannot be charged at all when placed in the charger.
I’ve set my DC power supply to 5V in preparation to connect to the lithium ion battery. This will be the target charging voltage.
I connect the 18650 battery to the DC power supply via alligator clips. I’m using a single 18650 lithium ion battery holder to hold the battery as it gets charged. You can also go ghetto and solder wire leads to it or my favorite is to use neodymium magnets on the positive and negative electrodes. Then just drop the alligator clips on the magnets. It’s also important to have a timer handy and make sure you don’t leave the battery charging unsupervised. Overcharging will kill the battery and potentially cause a fire.
Once the battery is connected, you can see that the power supply voltage drops to 3.7V. I’ve current limited the supply to 1A so that it doesn’t quick-charge the battery too fast. This can also create outgassing. You can also use a 5V, 1A DC wall wart to do the same thing without needing a fancy, schmancy power supply but it is much nicer.
After the 5 minutes are up, you can see that the batteries have now reached 3.367V. The batteries charge quickly up to this point because there’s not a lot of energy storage capacity between 0.5V and 3.0V. You can probably get there in around a minute of charging actually. Once you’re above 2.5V, its okay to slap it in a conventional battery charger.
Now I can just throw them in my rapid charger and charge it up completely.
No waste and you can salvage other people’s batteries that they think are dead. Yay!
Next stop…DIY Powerwall…
HI i have a question
So i have a li-ion cell with the same problem i started to charge it multiple times and at the 4th try the voltage stables in open circuit
does this mean this cell is recovered ??
It’s good to have the details of doing this manually. The cost of a fairly advanced 4-cell charger with a recovery function has dropped to around $30 though. The advantage is that the device will (hopefully) detect the kind of internal issues that cause undercharged li-ion batteries to explode on charging. I’d still throw together a fire-safe place to do it… A large plate with a glass or ceramic bowel on top (propped up a bit to vent) if nothing else.
connect the 18650 battery to the DC power supply via alligator clips. I’m using a single 18650 lithium ion battery holder to hold the battery as it gets charged. You can also go ghetto and solder wire leads to it or my favorite is to use neodymium magnets on the positive and negative electrodes. Then just drop the alligator clips on the magnets.
HI JUST BEAN READING YOUR FORM …LAPTOP BATTERY HOLDER SPLIT OPEN 12V FROM 6 INNER BATTERY’S .FOUND ONE DIED OK
I USED 4 JOINED TO GATHER 4.2V . THEN SOLDER SHORT WIRES ON THE PS/ NUT .CONNECTED TO MY METAL DETECTOR READING 3.5V
I HAVE BELL CHARGER . THINKING THE BATTERY’S NEED SOME CHARGE . TO GET THEM TO 4.2V .CHARGER LIGHT COME ON 6v orange
mains green light .left short time .green light on. that says fully charged . check battery volts .0.00 . to what you say the battery’s are ded ,is that so.
17 years ago in the USA they said they would solve the over charging . dose not look like it….i have some thing to tell you .but next time .
thank from john .
Worth mentioning there is a reason chargers don’t do this automatically:
Cells which have dropped below 2.5v may see an permanent increase in their internal resistance which can cause excessive heat during rapid charging or discharging potentially enough to cause a dangerous battery fire (especially when made into packs which concentrate heat in one area).
It’s fairly unlikely you will see this effect to any significant degree with good quality moderns cells but definitely good to be aware of the possibility. I have recovered my homemade 3 cell packs (made with cells manufacturered by Sony and purchased from a reputable vendor) I use with a remote control truck a number of times and never had a fire even though the truck can draw 70A at peak load. Just pay attention to cell temperatures for first few cycles after recovery and if they are getting hotter than normal I would get rid of them out of an abundance of caution.
Final note: chargers without a recovery function can still be used for recovery. Simply set charger to NICD setting, put it on a low current (I use .1a… Apparently the author is braver than I!) and start it… Don’t leave it unattended because the charging cut off for NICD is way higher than lithium cells so it will definitely over charge. Just let it sit until you have roughly 2.8v * number of cells you have in series then stop the charge, plug in the balance connector (if present) and charge as normal
I have a imax B6AC charger that brought back a 27 mV 18650 from the dead at .5A with the temp only reaching 36 deg C, don’t know how long the battery will last but it’s holding charge.
I had an old laptop battery lying around and decided to salvage the 18650s inside, but when I attempted tonput it into my charger that accepts any nickel or lithium battery, the display in the charger will only show an Error message. So I tested the each batteries and everyone only has 0.05v which is basically zero! no matter what I do, the charger won’t charge it so it’s impossible to wake it up.
What I did was, is to charge it using my $2 dollar cheap 18650 powerbank case from china. After few minutes, I removed the battery and checked the voltage and now it’s 1v+! so it has finally woke up. I then transferred them back to my multi-charger and now it charges them.
The only sad part here is that they don’t get up to full state of charge or 4.2v anymore, they just settle around 4.05-4.10v max after removing from the charger and measure their voltage after few minutes using a multitester.
But hey atleast they’re working now.
This process revived the battery on my Unistellar eVScope2 telescope. Thanks!