How far can LiIon be discharged?

I wouldn’t worry about self-discharge on a cell in storage or in a flashlight with no parasitic drain. I have 50+ 18650’s stored away that were at about 3.6v 5 years ago and some that I pulled last year were still around that.

If anyone wants to know how far a cell can be discharge and still perform well I recommend reading this entire thread.

I read a lot of datasheets with lots of opinion’s on the web and I have personally tested a lot of cells.
The thread above goes against everything I had read or was told. Not to say the datasheets are wrong but no data on what happens if the cell is subjected to outside of those specs. It’s a must read for battery Guru’s. :beer:

Thanks for the info HKJ. :+1:

I also still have the batteries in that thread at 10 years old now, I may do a discharge test just to see where they stand.
Anyone else still have some of these?

bluereidon, charge your batteries when you see fit. I usually do it below ≈3.6V, to always have some juice left.

Li-ion cell over-discharging is something I do not worry about. 2.5V is a frequently used and perfectly safe figure, even 2V for some chemistries. Those numbers can be found in top OEM cell datasheets.

I've recharged cells which were somewhat below 2V, from laptop packs. They can still work after this but I advice to keep them quarantined while whatching their self-discharge rate.

To me, the over-discharge thing is a busted myth, of course thanks to wisdom and discernment.

What really “hastens” battery/cell degradation is high voltage, and what I mean here is you can noticeably increase the number of useable cycles and life span by reducing the charge voltage. See BU-808: How to Prolong Lithium-based Batteries @ Battery University.

:-)

I recently purchased some 18650 cells and when I put them in the charger they were uncharged. Is this ok ? In the past, all cells that I have purchased have had partial charges when I received them.

Thanks,
Mike

Did you measure their voltage with a multimeter? What was their exact voltage?

If you’re reading zero volts, check both ends of the battery to see if there’s a thin clear plastic tab on it. Sometimes they put those on to prevent shorting or discharge during shipping. Obviously, they need to be removed.

If they’re protected cells, they’ll also read 0 volts if the low-voltage protection circuit has triggered. They might still be okay after activation.

If you’re reading something between 0 and 1 volt, I personally wouldn’t trust that cell. Under 2 volts, I’d still be a bit nervous of it, depending how long it has sat that low (and you don’t know how long).

The problem is not how far it works to be discharged, it’s about how far do you afford to do it.

Original Li-Ion spec is very clear: at 3.3V it is considered discharged and at 4.2 it is considered fully charged. Anything out of this interval will inevitably reduce lifetime. They do that to smartphones a lot: they overcharge to up to 4.35V.

Given the manufacturing improvements over the years, yes, the damage taken is smaller but it still happens: the cell will have less life-cycles.

So when choosing how low you want to go with a discharge, you practically establish the life of your cell.

Does this mean that for laptops, cellphones and powerbanks, its bad practice to discharge Li-Ons below 10%?

Generally yes.

If you want super extended lifetime for you phone battery you can stop charging at 80% and don’t discharge it all the way. In fact, most phones will try to stop you from discharging completely (have failsafes at around 15) as getting too low may not provide sufficient current for normal functionality anyway. Some battery-related applications also recommend charging only up to 80 which corresponds in most cases with the 4.2V value.My article about phone batteries here.

On the laptop side things are a little more elaborate. Laptops will not overcharge Li-ion cells as far as I’ve tested until today, but they have another problem: most models except the high end and top ones have low quality or even no charge/discharge BMSs. That will mean in time (taking a 3 cells in series battery as example) that a pair of cells will start not getting enough charge, another will remain balanced and another will overcharge, leading to 2 / 3 cell pairs starting to degrade faster and faster. That is one of the main reasons of current laptop batteries dying so fast.
In the case of laptops I only use them on battery when really needed and I don’t cycle the battery as some do because cycling does lower lifetime compared to not doing it.

While I agree with many stuff in Overmind's article, I believe differently in certain areas. The discharge cut-off thing, namely.

The industry standard for li-ion cell discharge cut-off nowadays is 2.5V, even though older and/or high voltage energy cells usually set it higher. Examples: Samsung ICR18650-30A/30B/32A specify 2.75V cut-off, LG ICR18650-C2/D1 specify 3.0V cut-off, LG ICR18650-E1 2.75V cut-off, LG INR18650-MJ1 2.75V cut-off…

In essence, the selected cut-off voltage for a cell or battery is, in my opinion, the highest voltage which allows delivery of the battery's minimum specified capacity at its maximum specified discharge rate or current.

I also take great care of smartphone batteries, being a heavy user of these devices. I run a rooted custom Android ROM and pay great attention to power handling and consumption, clipping the wings of certain apps and uninstalling any unneeded bloat if required. With 3C Battery Monitor I enjoy battery usage graphs, history and even statistics. I do not usually charge above ⅔ of the fuel gauge, but don't hesitate to go all the way down to 0%. Smartphone batteries do have built in BMS circuitry and cut-off properly, no need to care for this. In fact, in all my rooted Android devices I disable the low battery warning (works by disabling System UI notifications).

The cells that I purchased were new and appeared to have no, or very little charge. I asked the dealer (IMRbatteries) if they were ok and they said to charge as normal. They charged fine, but I don’t like to take chances with li-ion batteries and I value the information from the forum members here more than the dealer. So I will probably discard them.

Thanks,
Mike

mikeyx li-ion batteries often ship with relatively low voltages, I think this is due to transport regulations.

What cells? What voltage? Multimeter measured, doesn't it?

Some of you seem overly dramatic with the low voltage thing, but in my experience it really is a myth. I've salvaged laptop cells with really low voltages, even a few slightly below the 2V threshold, and they ended up working well. After initial discharge tests to verify their performance I further charge them close to 3.9V, measure and write down their resting voltage at least half an hour after this, and them let 'em rest a few weeks. Finally I measure their voltage again and compare to the initial figures. This is a good integrity check as healthy cells will barely show any self-discharge, few millivolts at most.

Wed, 10/02/2019 - 21:29

I get the feeling mikeyx didn’t measure the voltage with a DMM. Maybe he just relied on what the charger said, but most chargers are horribly inaccurate.

When I buy new cells, the first thing I do is measure their voltage. All good ones arrive at somewhere between 3.3v and 3.6v. They ship at a low charge for safety reasons.

As Barkuti says, then you should probably test them. I do what he does, but instead I fully charge to 4.20v. After a week or so, they should still be above 4.16v. Voltage will drop some initially, which is why they don’t hold a full 4.20v, but after a few hours, they should maintain voltage pretty well. If you use 3.9v as Barkuti does, they should hold rock-solid after the initial drop when you remove them from the charger.

I have many cells in storage at 3.75v, and they hold that way for years.

If you see any cells self-discharging at an unusually high rate, they’re bad.

Also, feel the cells often when you first charge them. They should never get hot. That also indicates they’re bad (assuming you’re not charging at too high a current).

Unless you know what their voltage was at the time, you really cannot judge their state of charge/discharge with any sort of accuracy.

I have a head light, which somehow is capable to discharge protected batteries to around 2.8V. Maybe even lower, but I am not sure. It is measured by the charger before I start charging, and there is no sign of recovery like in the pictures (which is applicable to any battery type anyway ).
Those batteries are in better condition according to the charger than some of my other batteries, which are just put away unused. :open_mouth: The unused batteries are also show very different behaviours: from almost still fully charged to completely destroyed state…

Still, I think LiIon batteries are superior to NiMH and especially to NiZn batteries.

Your headlight has bad ‘parasitic drain,’ so keep batteries out of when not using.

Chris

Even if the battery is protected (i.e. features a built-in 1S BMS circuit), the headlight can still discharge it down to 2.8V or even lower, if it allows it. This is because the actual discharge voltage limit is the BMS cut-off voltage which, according to a few datasheets of the DW01 controller I have lying around, is 2.4±0.1V (datasheets parameter is “VODP” or over-discharge detection voltage). The DW01 is by far the most common 1S BMS (or single cell) protection circuit.

This is good advice. :THUMBS-UP:

Still, RelakS may want to measure how bad the parasitic drain is:

First take the amount of cells your headlight uses (cells in good health, of course), set them ready with some useable amount of charge, and measure their voltage with a voltmeter before inserting them into the headlight. Note down the cell voltages prior to headlight insertion, along with the insertion time and date, and then insert them into the headlight. Wait a few days. At the end of the few days, extract the cells and note down the extraction time and date. You can also inmediately measure the cell voltages and note it down for comparison purposes (you can also measure cell voltages again after a few minutes out of the headlight, just to check, but it should be the same).

The voltage difference (cell voltage before insertion minus cell voltage after extraction) divided by the elapsed time provides you with some insight about the headlight parasitic drain.

P.S.: of course use the same voltmeter for all the test involved measurements.

I accidentally discharged eight DMEGC 26E 18650's much lower than expected one night back in August. A very hot night here in south Texas which didn't help the situation. They were so hot, I could barely touch them. In a panic, I threw all of them in the freezer and hoped for the best. I was seriously expecting fire works. It took much longer than expected, but they did finally cool down. When I checked the first one with my Fluke multimeter, I was shocked (figuratively)......1.2 volts!! Because I didn't want to leave them at that low of a voltage until the next morning when I could drop them off at a local business that accepts used batteries for recycling, I decided to throw them on the charger to see what would happen. I charged them up to 3.7 volts and left them all in the kitchen sink overnight. They looked fine the next morning and all had held their charge. It seemed as if they were ok so I decided to fully charge them and use them. They seemed to be operating normally. I've been using all of them since. No problems. I have a total of 25 of them and the 8 that got abused perform just as well as all the rest. 16 of the other brand new ones are used as a boost pack for my electric scooter. The other 9 (there was one extra) are being used for my flashlights.

I think I got lucky. Don't try this at home.

X Ray, that is to be expected. Just because a cell is over-discharged does not mean that it will get damaged. It takes time for this to happen. I once recovered a few Samsung (26C) cells from a laptop pack whose voltage were at 1.6V or a little bit more (out of 6 cells most were below 2V, and who knows how much time they were left this way). After recharging to a healthy voltage (≈3.9V), I left them at rest for 2 - 3 weeks to observe self-discharge. I ended up discarding two cells, as I noticed a little bit of self-discharge in them. All of the remaining four were put into service.

Cells do not die that easily. And if you know how to take care of them, all will be safe.

Can anyone tell me whether or not my Manker 18350 is still safe to charge and use?

Ive accidentally disharged it to 2.6v

Mankers website says the lights that use this cell (E14III & MC13) operate at a “working voltage 2.8-4.3v”
(Below is a screen shot of that quote from their website)

The battery/cell itself also says “Built in charging circuit prevents overcharging, over-discharging and over-discharge current.”
(Pics of the cell/that quote below)

I was using the light when it flashed the LVP warning and dropped to low brightness. I then stopped using it and put it away.
I then forgot about it for maybe a week or two without charging it back up… Oops.

Im pretty sure LVP warning happened at about 2.7v.
Checking the voltage now though shows 2.6v on my DMM, and Im unsure if its safe to charge and continue to use.

Side note: Im also now wondering what the difference is between “over-disharging” and “over-disharge current”.

Advanced thanks to anyone who can help me out here.

Charge it & use it. All is well.