Using older batteries

[Axxe]

Hello everyone,


first post here (in three parts) - but long-time lurker in this (sub-)forum And now finally registered as I have questions about li-ion batteries, hoping someone has some thoughts on them. I just read the forum rules and concluded that to comply with rule 13c I need to split it into three different threads to avoid a cluttered thread with a meaningless title.
I apologize if that was incorrect and ask for merging the threads if that was the case.


So in this thread only the things about the usage of older cells and not those questions that I ask only to cure my curiosity.



1) Are older cells just (potentially) annoying or are they "unsafe"?

I do know (from watching Mooch's YouTube videos) that it's incorrect to phrase it as "safe" or "unsafe" as there's always a rest risk using li-ion cells and that it's not a binary thing "either safe or unsafe" with nothing in between.
But the approximate amount of how much the usage risk increases interests me. Let's say I use an older cell that lost a noticable amount of capacity - is the danger involved in doing so more like "didn't tie my shoe correctly" or rather like "driving 200 mph in the wrong direction" when compared to a newer cell?
Background of this question: I have some older cells that definitly lost quite some capacity, but they're still useful for what I use them for (low watts regulated), they don't get warm during charging or using, the IR is higher than on younger cells of the same type but nothing too extreme.

Just three examples:
VTC6, 6 years old, useable capacity around 1500 mAh, IR 97 mOhm. -> Recycled.
VTC6, 6 years old, useable capacity around 1600 mAh, IR 61 mOhm. -> Was still in use, now pending recycling. Would using it be a high risk compared to a newer cell? (<-- I don't intend to do so! I'm asking out of curiosity.)
VTC6, 5 years old, useable capacity around 2300 mAh, IR 27 mOhm. -> Still in use. I'd say "old but healthy"...right?

Spoiler: What I mean with "usable capactiy" and how I measured it & the IR

- "Usable capacity" = my way of saying that this is the amount that was recharged after using the cell until the mod gave battery empty message as I don't know the correct term for that
- both mAh and IR measured by one of my Miboxer C4-12 upgrade, after I checked both charger's accuracy by comparing their IR reading of new cells with the datasheets of the batteries;
- the contacts in the chargers get cleaned with isopropanol prior to every usage and
- I regularly recheck the charger's accuracy by (cross-)comparing the readings with each other, with previous readings and by comparing the readings of new cells with the cell's datasheets and / or Mooch's average measurements of the specific model)

2) Internal Resistance

I'm wondering why the last cell mentioned still has such a low IR on the same level as a new VTC6, despite its age and usage - leading me to the question if the IR is actually (together with the capacity measurement) useful to determine the status of the cells to help deciding when to take a cell out of use or not.



Any thoughts on that would be highly appreciated and thanks for reading!


Greetings,

Axxe

 

[puffon]

Good question.
I'd like to hear what @Mooch has to say when he has time and sees this.

 

[no|ah]

Also curious about this.

Edit: From what I'm reading, it seems that low mAh can mean anything from imminent failure to just a tired battery, and that internal resistance is still a useful metric. This was an interesting article about checking if old 18650 batteries are still good.

How true any of that is, I'm not sure, and would definitely be interested in what an expert like Mooch has to say.

 

[DPLongo22]

I'm no expert and I'm CERTAINLY no Mooch. I can only tell you my own personal experiences over the past 12+ years.

I've been cycling batteries throughout, mostly 18650s, with some 16340s and now 21700s thrown in. Barring damage, which gets addressed IMMEDIATELY (no exceptions), I usually run them for anywhere between two and four years before I start seeing degradation (charges don't last, etc.).

Unless they're damaged, I've never thought them to be "unsafe".

I treat ALL batteries with the utmost respect, and always have. This includes measly little AA & AAA too, with special attention to 9Vs, because, "Kaboom!" sucks. I don't "drop" them into mods or flashlights, and always make sure to check on things that stay in devices (mods, flashlights, tools, etc.) for long periods of time. They corrode, which is about the lowest level of battery-related problems to have.

This is all just one very uneducated man's opinion. Do with it what you will, with "Ignore" possibly being the best option.

 

[englishmick]

Not something I worry about too much since batteries aren't that expensive. I recycle them after 3 years, assuming nothing bad happens with them. My charger does do the measurements, but it takes 5 hours to run in that mode so I don't do it often.

I keep the retired ones in a box to use for recharging cell phones during power outages.

 

[Axxe]

I'm no expert and I'm CERTAINLY no Mooch. I can only tell you my own personal experiences over the past 12+ years.

I've been cycling batteries throughout, mostly 18650s, with some 16340s and now 21700s thrown in. Barring damage, which gets addressed IMMEDIATELY (no exceptions), I usually run them for anywhere between two and four years before I start seeing degradation (charges don't last, etc.).

Unless they're damaged, I've never thought them to be "unsafe".

I treat ALL batteries with the utmost respect, and always have. This includes measly little AA & AAA too, with special attention to 9Vs, because, "Kaboom!" sucks. I don't "drop" them into mods or flashlights, and always make sure to check on things that stay in devices (mods, flashlights, tools, etc.) for long periods of time. They corrode, which is about the lowest level of battery-related problems to have.

This is all just one very uneducated man's opinion. Do with it what you will, with "Ignore" possibly being the best option.

Thank you for your answer!

And yes, I use the same principles when dealing with batteries. If a charge doesn't last - if there's any amount of self-discharge, even just a bit - the battery gets sorted out for recycling immediatly.
Also I have my personal "box law": a li-ion cell is either in a device or in a box with no exceptions; and the tiniest damage to its wrap will make me rewrap them.

So to be precise - my initial question is in regards to cells that aren't damaged, but just old & tired without self discharge.

 

[Mooch]

1) Are older cells just (potentially) annoying or are they "unsafe"?

Both.
They can be annoying and, if the conditions are right, they can be less safe than they were before. Under certain circumstances a cell can be outright dangerous to use.

Unfortunately there’s no way to quantify the risks for any particular cell. All we have are “best practices” and our individual tolerances for risk.

But unless they are overcharged, overdischarged, or charged when too cold, IMHO most cells will just become annoying to use without much additional risk.

Edit: From what I'm reading, it seems that low mAh can mean anything from imminent failure to just a tired battery, and that internal resistance is still a useful metric.

It can be useful but typically doesn’t change much compared to the loss of capacity as the cell approaches the end of its useful life. The capacity could drop 40% but the IR would drop only 10%-15%

Something to watch out for…AC vs DC IR.
Unless you’re carefully reading the datasheet you might miss that the spec is a max (not typical) and that it’s AC IR. It’s determined by injecting a 100mA, 1kHz sine wave into the cell and measuring the resulting voltage swings. From that, using Ohm’s Law, you can determine the AC IR. Roughly, it indicates the “health” of the cell’s electrolyte.

This is a lower number than the DC IR you get using your charger. The DC IR is determined by pulse discharging the cell into a load (typically a resistor) for a few milliseconds and noting the voltage sag. Use Ohm’s Law again to determine the equivalent resistance.

Soooo…the datasheet’s IR number can’t be used unless you have a YR-1030 meter or some other AC IR meter. And most chargers are spectacularly innaccurate when reading DC IR.

If you take the same cell and take three IR readings with your charger, removing and reinserting the cell each time, are they all within a fraction of a mOhm of each other? If more than a mOhm apart then the results aren’t very consistent. A couple mOhms apart and they’re getting pretty useless.

How about readings taken on different days? Do you charge each cell to the same point the same way and take the readings with the cells at the same temperature? This is critical.

Bottom Line: capacity loss is typically the best way to track cell health for most people. The manufacturers say a cell has reached the end of its life when at 60%- 80% (check the datasheet) of its rated capacity. It’s up to you though when to retire a cell.

 

[Mooch]

if there's any amount of self-discharge, even just a bit - the battery gets sorted out for recycling immediatly.

This can also be a good way to determine if a cell is badly damaged or nearing the end of its life.

Charge the cell very slowly, let sit at room temp for at least a day, check its voltage to the nearest mV, let the cell sit at room temp for at least a week, recheck its voltage. If you’re below 4.15V or so then the cell is probably self-discharging faster than normal. That’s not a disaster but can be another data point to consider when deciding whether to retire a cell.

Doing that to several cells at once is a great way to sort out the more damaged/aged cells since you get to compare them.

If the cell has dropped below 4.0V after a week though then IMO it’s time to recycle that cell.

 

[Axxe]

Thank you so much for your answer and the time and effort you put in it, Mooch! It really helps me a lot for my decision on how long I use my batteries and when I will retire cells.

About the internal resistance: If provided I use the DC value from the datasheet, if not provided I use the average that you measured in your cell tests and if you haven't tested the cell I use the AC value from the datasheet.
As I don't have a resistance meter I use the measurements from my chargers as I had used the IR until now only as a rough guideline, trying to get an idea about how "worn out" the cell is. To do so I have a list and when I get new batteries I charge them, use them until cutoff by the mod, recharge them and note the date, mAh and IR. By comparing measurements in the future with these notes I tried to get an idea about how "worn out" a particular cell is. That was how I came to this question as I was asking myself if this procedure is actually useful.

It can be useful but typically doesn’t change much compared to the loss of capacity as the cell approaches the end of its useful life. The capacity could drop 40% but the IR would drop only 10%-15%

That explains the old VTC6 I mentioned with notable capacity loss but surprisingly low IR! And I was actually wondering why that is for quite some time

And most chargers are spectacularly innaccurate when reading DC IR.

If you take the same cell and take three IR readings with your charger, removing and reinserting the cell each time, are they all within a fraction of a mOhm of each other? If more than a mOhm apart then the results aren’t very consistent. A couple mOhms apart and they’re getting pretty useless.


How about readings taken on different days? Do you charge each cell to the same point the same way and take the readings with the cells at the same temperature? This is critical.

The three reading-test is actually something I have done - not scientifically exact, but by comparing the IR after the first recharge with the one after subsequent recharges. The difference is usually about 1-3 mOhm and for newly bought cells the reading is usually in the range of the value from the datasheet and / or your test report. The readings are quite consistent between both chargers (Miboxer C4-12 upg.).

I use the same charging current and the temperature of the cells is always room temperature, and I clean the contacts of the chargers and the batteries with isopropanol prior to charging.

Until now I have used these values only as a rough estimate to see in which range a cell is (like i.e. a new VTC6 that I measured with 22 mOhm compared to an old one that read around 97 mOhm). If I understand you correctly these readings aren't useful for anything more than that as they are too inaccurate?


About the self-discharge: Here I just use the most inaccurate method - I look at what my mod tells me as I thought that if it's noticable enough to see it even on the battery bars of a mod than it's bad enough to recycle that cell.
(That was how I discovered that something is very wrong with the cells I mentioned in the other thread - both were fully charged, after 2 weeks I put them in a mod and one cell was 100% and the other 60%. After putting them in the charger the first one was detected to be full and the other one took as much as approx. 40% of the rated capacity..)


Again I want to thank you very much that you took the time to write your comprehensive answer that really helps me a lot!!

 

[Mooch]

Until now I have used these values only as a rough estimate to see in which range a cell is (like i.e. a new VTC6 that I measured with 22 mOhm compared to an old one that read around 97 mOhm). If I understand you correctly these readings aren't useful for anything more than that as they are too inaccurate?

If you’re getting 22mOhm consistently for that cell then you’re fine, that is very close to what I get (check the Ratings & Performance table for the number, I’ve forgotten). Your charger(s) are considerably more accurate than the ones I have tested….which is great!

But even if they weren’t accurate that wouldn’t matter as long as they are consistent. That still allows you to track IR changes over time and compare cells.

 

[Axxe]

That's really helpful, thank you for your efforts, Mooch!