Reviving dead lithium cells - Page 1
Forum section: electronics / general

author: Connecteur
author_rank: Frequent Contributor
timestamp: September 15, 2025, 11:04:53 am
content: I bought a small powered screwdriver in 2017. After sitting unused for a few years, it no longer was taking a charge. I opened it up, and it had a single 18650 (LiFePO4 ) battery. I gave it a shock charge of 30V to get it started charging again. It's all back to normal now.This is not dangerous, because LiFePO4 chemistry does not easily catch fire.

author: paulca
author_rank: Super Contributor
timestamp: September 15, 2025, 11:15:53 am
content: DO NOT TRY THIS AT HOME..... or anywhere without PPE.Next time try 3V current limited to 10mA and be patient.

author: Connecteur
author_rank: Frequent Contributor
timestamp: September 15, 2025, 01:30:55 pm
content: I limit the current to about 100 mA, but I raise the voltage until I see it taking some current. Once it gets charging, I reduce the voltage to 3.7V, or whatever the rating of the battery.

author: rteodor
author_rank: Frequent Contributor
timestamp: September 15, 2025, 01:49:05 pm
content: Did you measure how much of the rated capacity it holds ?

author: Connecteur
author_rank: Frequent Contributor
timestamp: September 15, 2025, 03:11:05 pm
content: Quote from: rteodor on September 15, 2025, 01:49:05 pmI'm not concerned about that, as much as restoring the ability to charge.

author: rteodor
author_rank: Frequent Contributor
timestamp: September 15, 2025, 05:51:02 pm
content: Quote from: Connecteur on September 15, 2025, 03:11:05 pmI am curious how LFP recover after over-discharge. Li-Ion and Li-Po cells I tried to recover did bad. Like a third, sometimes less than 10%.Did you at least measure the voltage before jolting it ?Quote from: paulcaFor such tiny cells I would be more concerned if high voltage could damage the over/under-voltage protection circuit (if its there). Such damage may lead to a later disaster.

author: Connecteur
author_rank: Frequent Contributor
timestamp: September 15, 2025, 06:07:07 pm
content: There may have been a few microvolts before the treatment. I did not apply 30V while the cell was unattended. I watched the amperage of charge rise to 100 mA, and then reduced it to 3.7 V.

author: Geoff-AU
author_rank: Frequent Contributor
timestamp: September 16, 2025, 12:27:51 am
content: Quote from: Connecteur on September 15, 2025, 11:04:53 amTo recap, you applied 30V to a 3.7V cell, and then continued to charge and use it without checking self-discharge rate or remaining capacity...I would caution anyone reading it against taking the word of some random person on the internet without applying their own critical thinking skills first.

author: thm_w
author_rank: Super Contributor
timestamp: September 16, 2025, 02:04:39 am
content: In the future just set the supply to 3.7V, ZERO reason to set it to 30V, terrible idea.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 16, 2025, 08:43:31 am
content: With a single cell recharging from dead may work. If there are more cells in series, one should make sure the balance is somewhat OK. Otherwise one cell may get overcharged, while the other is rather empty. With a small screw driver chances are it is single cell.

author: paulca
author_rank: Super Contributor
timestamp: September 16, 2025, 10:16:45 am
content: The risk is normally that crystal dendrites grow on the electrode at low voltage. Depends on chemistry.When a crystal grows from one electrode through the electrolyte it lowers the insulation between the electrodes.Applying 30V to a cell in a bad state is just asking for it to begin to microshort and eventually go thermal run away.It is the chemical degradation resulting in the LOSS OF SAFE OPERATING CONDITIONS inside the cell which is why the common message is to "Bin them if flattened below spec."Sure you can recover them, but you should never trust them, not even idle. Best is to put a 1k resistor across the cells, put them in a window with a candle and pay you last respects.EDIT: This advice is even more appropriate if you are using "packaged" cells, like 18650s. The reason being, you are even further from the thruth than say a "pouch cell". I recovered a 800mA 12.6v pouch cell from an RC plane that got stuck in a tree for 2 days. It was 0.8V per cell when retrieved. I trickle charged it to 2.7V, then set it to 4.2V per cell 1 Amp and when it got towards full charge I stopped it and immediately discharged it. Why? The pouch had swollen considerably. This suggests that degassing is occuring in the cell. It's normal over repeated use, but any direct swelling during charge and ... bin it.As 18650s are in a pressurized metal can you will not see the cell swell, so you won't get that warning.

author: Berni
author_rank: Super Contributor
timestamp: September 16, 2025, 11:05:39 am
content: As said above, do NOT revive long dead lithium cells.When sitting empty these cells degrade internally, they might still charge up fine, but then as you let it sit for a few days charged it could spontaneously burst into flames.The way to recover batteries is to disassemble packs into cells, test individual cells then combine the cells that are tested good into a new pack. By testing means checking the initial voltage not being too low, capacity matching reasonably well, internal resistance matching etc..

author: Connecteur
author_rank: Frequent Contributor
timestamp: September 16, 2025, 12:17:23 pm
content: "Don't do anything, there may be some risk."

author: paulca
author_rank: Super Contributor
timestamp: September 16, 2025, 12:23:39 pm
content: Quote from: Connecteur on September 16, 2025, 12:17:23 pmPouring a kettle of water into a cup while in bare feet "there may be some risk".Putting your hand in the fire. There may also be some risk.Lithium battery fires are very real, very common, very hard to stop and utterly destroy, as a minimum the room they are in. Unless you find a way to remove the battery IMMEDIATELY or contain the fire its game over, call 911. They have involved fatalities.Even small packs. I spent long enough on "Radio controlled" modelling forums to see too many sad photos of peoples workshops in blackened tattered remains after the fire department had left. The 10s of thousands bill to repair the house etc.

author: Connecteur
author_rank: Frequent Contributor
timestamp: September 16, 2025, 04:06:30 pm
content: Of course, I'm just an idiot who can't possibly manage to do anything without hurting myself, right?

author: Berni
author_rank: Super Contributor
timestamp: September 16, 2025, 05:15:02 pm
content: The actual process is not really that dangerous, just keep the cells somewhere non flammable.More the danger is that the cells sometimes recover and appear to be fine, but in actuality are ticking time bombs that threaten to burn down your house when you are no longer careful and just store it as any tool in a drawer. Not something that is worth the few bucks that a 18650 cell costs.

author: Ian.M
author_rank: Super Contributor
timestamp: September 16, 2025, 05:25:05 pm
content: Also the remaining capacity of a 'recovered' cell that has been deep discharged for an extended period is usually cr@p, so it wont be fit for purpose even if you don't care about safety.

author: MK14
author_rank: Super Contributor
timestamp: September 16, 2025, 05:45:58 pm
content: Quote from: Siwastaja on September 16, 2025, 10:41:05 am

author: Connecteur
author_rank: Frequent Contributor
timestamp: September 16, 2025, 08:07:17 pm
content: Are you aware that LiFePO4 cells are much safer than the old type, and do not catch fire very easily at all? Secondly, when you set the current limit low, and raise the voltage until current starts flowing, there's no chance of of a thermal runaway. When the current starts to flow, drop the voltage to 3.7V, which will not overcharge the cell.This could be a useful technique for someone who wants to restore some life to a cell to some degree of usefulness instead of throwing it away.To imply that I don't know what I'm doing, and this procedure is dangerous, is an insult you should feel ashamed of making.

author: MK14
author_rank: Super Contributor
timestamp: September 16, 2025, 11:28:38 pm
content: Quote from: Connecteur on September 16, 2025, 08:07:17 pmPlease show me where the manufacturers of such batteries (or other sources, of very reliable, expert advice), recommend such procedures?

author: MK14
author_rank: Super Contributor
timestamp: September 17, 2025, 12:01:45 am
content: Quote from: Connecteur on September 16, 2025, 08:07:17 pmThen please explain the following, fairly recent video. Which seems to show, the same chemistry type of battery, you were using. Exploding, and there was a fire!

author: Connecteur
author_rank: Frequent Contributor
timestamp: September 17, 2025, 01:23:22 am
content: Quote from: MK14 on September 16, 2025, 11:28:38 pmNowhere at all; I came up with it myself. What is your point?

author: Gyro
author_rank: Super Contributor
timestamp: September 17, 2025, 08:30:39 am
content: Quote from: Connecteur on September 17, 2025, 01:23:22 amFrankly if I'd 'come up' with abusing a "dead" Lithium cell into accepting some charge to an unknown remaining capacity, with probable internal cell damage that could come back to bite me in the future, I wouldn't even have bothered posting it. Maybe we have different levels of what we consider to be of value.

author: Connecteur
author_rank: Frequent Contributor
timestamp: September 17, 2025, 08:33:38 am
content: Quote from: Gyro on September 17, 2025, 08:30:39 amFears do not create hazards, especially imaginary ones like this.It's more dangerous to cross a street.

author: paulca
author_rank: Super Contributor
timestamp: September 17, 2025, 10:04:38 am
content: Just, please, take these risks alone with nobody or nobodies property near by.

author: Gyro
author_rank: Super Contributor
timestamp: September 17, 2025, 10:58:54 am
content: Quote from: Connecteur on September 17, 2025, 08:33:38 amYour reply doesn't seem to bear any relationship to my post.'Fooling' the charging circuit by briefly elevating the cell voltage with a Frankensteinian high voltage pulse and then claiming 'It lives!' has no validity. The designers of Lithium cell charger ICs deliberately refuse to charge undervoltage cells for safety reasons (over millions of products sold). To set these voltage thresholds, rather than just charging regardless of cell voltage, takes up die area (micropower threshold reference, comparators etc.) This extra die area adds up to significant money over millions of ICs, for low cost commodity IC manufacturers. It there was no need, they simply wouldn't bother.That you might have got away with it on a single cell sample means precisely nothing in the context of the vast array volume manufactured products, and should not be recommended or defended on a public forum. Ask millions of people to cross the street without looking and see what happens.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 17, 2025, 11:22:27 am
content: How about applying mains voltage instead? The higher the better, obviously, would you agree?

author: Connecteur
author_rank: Frequent Contributor
timestamp: September 17, 2025, 12:10:35 pm
content: Quote from: Siwastaja on September 17, 2025, 11:22:27 amIt's sad that I should expect to be attacked as either stupid or dangerous, no matter the subject.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 17, 2025, 12:34:59 pm
content: Besides, a screwdriver from 2017 would have been very unlikely to use LFP cell in 18650 form factor; just bog standard LCO, NCA or NMC cell. But OP of course knows that, just like heknowsthat Sony Discman does not use lead acid batteries, and mystery laptop from 1990's didn't use rechargeable alkaline cells.

author: paulca
author_rank: Super Contributor
timestamp: September 17, 2025, 12:58:43 pm
content: The 4.2V has a 100mV tolerance on it. Beyond that you are in dangerous territory.Again most of my experience is with "high current pouch lipos" or large prismatic LFPs.In RC land I have seen people explode batteries with only 4.35V and 20Amps. In that case the current just accelerates what is already happening at 4.35V

author: Connecteur
author_rank: Frequent Contributor
timestamp: September 17, 2025, 01:00:46 pm
content: Quote from: Siwastaja on September 17, 2025, 12:34:59 pmOf course, I'm an idiot, if that's the type of person you want to be.

author: paulca
author_rank: Super Contributor
timestamp: September 17, 2025, 01:18:14 pm
content: Did you try the traditional trusted method before you applied this custom 30V technique?Where did you get the 30V technique?Did you make the post knowing it would get flamed and went ahead and did it anyway, for lolz?Anyway. I'm interested in the results.Give us your measurements:Voltage before recovery and current/impedence you measure it under.Charge profile used to recover and fully charge.Several charge/discharge cycles with capacities.Several days stored fully charged warm or cold for self discharge.

author: Geoff-AU
author_rank: Frequent Contributor
timestamp: September 17, 2025, 11:27:22 pm
content: Quote from: Connecteur on September 17, 2025, 01:23:22 amSo you did it once and the outcome was OK. You're aware of Russian Roulette, right?

author: Connecteur
author_rank: Frequent Contributor
timestamp: September 18, 2025, 10:07:27 am
content: Quote from: Geoff-AU on September 17, 2025, 11:27:22 pmSure, with a cylinder with a thousand chambers.

author: Gyro
author_rank: Super Contributor
timestamp: September 18, 2025, 01:00:30 pm
content: Professional designers have to plan for a hell of a lot more chambers than that, something that you seem incapable of understanding. A few blow-ups and it's a massive recall (assuming you don't burn somebody's house down and kill them, then things get really nasty!). Your screwdriver was designed to avoid such occurrences, hence it refused to charge a dead cell.Professional engineers do not have the luxury of 'pratting about' like you do. Wehaveto do things safely - and not brag about getting away with doing stupid thing on the internet.Pleaseat leasttryto understand.

author: armandine2
author_rank: Frequent Contributor
timestamp: September 18, 2025, 01:24:18 pm
content: ...engineering truthshttps://en.wikipedia.org/wiki/No_Highway..reminds me of my mech-eng mate who pointed out the crack in his window - plexiglass, on a commercial passenger airline

author: mtwieg
author_rank: Frequent Contributor
timestamp: September 18, 2025, 01:26:34 pm
content: Quote from: MK14 on September 17, 2025, 12:01:45 amThis video makes the important distinction between hazards due to the cells themselves entering thermal runaway, and the cells emitting flammable gasses (mainly hydrogen). The video recognizes that thermal runaway is much more unlikely for LFP vs other Li-ion chemistries. But also says that the risk due to outgassing hydrogen is higher with LFP. After a bit of google searching, I've found the same claim roughly from several other sources. Not clear whether this is an issue with a properly functioning BMS or not, though.

author: MK14
author_rank: Super Contributor
timestamp: September 18, 2025, 01:44:17 pm
content: Quote from: mtwieg on September 18, 2025, 01:26:34 pmMy understanding/interpretation, but it could also involve reading between the lines and/or introducing things they didn't say in the video. Is that the battery management system, can fail and/or be damaged (e.g. humidity/damp/water and other things, that can effect/damage electronics). Hence making the batteries vulnerable again, to dangers. Also, the BMS is probably neither perfect or fool-proof.E.g. An important FET, as part of the protection, goes short-circuit (perhaps because of self-heating over time) and/or electrolysis (damp) causes shorting growths, perhaps over many years, across important points, in the circuit.

author: Connecteur
author_rank: Frequent Contributor
timestamp: September 18, 2025, 01:56:10 pm
content: I'm guessing that your mommy never let you use the pointy scissors.

author: MK14
author_rank: Super Contributor
timestamp: September 18, 2025, 03:40:02 pm
content: Quote from: Connecteur on September 18, 2025, 01:56:10 pmEdit:Better safe than sorry!

author: Gyro
author_rank: Super Contributor
timestamp: September 18, 2025, 05:27:12 pm
content: Quote from: Connecteur on September 18, 2025, 01:56:10 pmThat the best you can manage? No even vaguely technical points? Rather sad and pointless then.

author: Geoff-AU
author_rank: Frequent Contributor
timestamp: September 19, 2025, 01:24:20 am
content: Quote from: MK14 on September 18, 2025, 01:44:17 pmIf you put too many packs in series, and one pack's BMS tries to open up, the voltage of the whole stack appears across the one MOSFET and yes it'll usually fail short and silently stop protecting its part of the stack.

author: Simon
author_rank: Unknown
timestamp: September 19, 2025, 04:51:00 am
content: I ignored the first report on this thread as the usual had happened. A post that merited removal became a discussion and a heated one with both sides more or less as bad as the other. Now it's just getting silly.If you want to report a thread like this then don't post in it. The more people pile in the more it becomes likely the thread will stay up.