Li-Ion at 3.5v when in storage

[WalkIntoTheLight]

I highly doubt they still have 75% life left if they were kept fully charged most of their life. You'd be lucky to still have 75% even in the best possible conditions.

5 of 6 cells measure about 1800mAh, 1 cell about 1600mAh. They were originally 2200mAh. Samsung 22F. I think they're 10 years old, but I could be wrong... might be closer to 9. I bought it sometime late last decade.

The HP laptop was popping up a warning to replace the battery during its last couple of years. The run-time was way down, probably less than half. That is why I was surprised that the individual cells measured so high.

Maybe HP warns about the battery and reduces output after a certain number of years? Or maybe it was something else, other than capacity.

Keep in mind that the industry standard definition of "end of life" is the point when the cell degrades to 80% of nominal capacity. Most studies don't consider what happens after that point.

Yes, that's what I'm wondering about. Perhaps degradation slows way down after the first 20%.

20% degradation in one year can certainly occur in poorly managed cells, e.g. that's exactly what happened in said Dell laptops (whose batteries were kept close to fully charged by the laptop and often at elevated temperatures - both of which greatly accelerate degradation).

Yes, I know the heat + full charge state in laptops are about the roughest you can do to lithium-ion batteries. I've generally had pretty-good luck with laptop batteries, though. They definitely drop their run-time, but I've never had one get so bad it's unusable. Maybe I don't run them that hot, since I usually just use laptops for Internet browsing.

 

[Gauss163]

^^^ Yes, if you used them in a way that kept them cool and lowered their average lifetime charge (possibly helped by HP battery saver software) then that may explain why you got better life. What discharge rate did you use to get those capacities?

Dell is probably near worst-case since they delayed doing battery management in order to maximize profits from battery sales.

 

[WalkIntoTheLight]

^^^ Yes, if you used them in a way that kept them cool and lowered their average lifetime charge (possibly helped by HP battery saver software) then that may explain why you got better life. What discharge rate did you use to get those capacities?

500mA, IIRC. There was no battery-saver function on that laptop. But since I didn't use it much the last couple of years I had it (before taking apart the battery pack), it might have been below 100% charge for some of that time. For the first several years, it definitely was 100% charged most of the time.

It's possible that "100% charged" isn't 4.2v per cell. Though, I'd find that surprising, since the laptop makers want to brag about run-time, and don't really care if the battery lasts past the warranty period. The battery-saver modes in my newer laptops very clearly indicate the charge as 80%.

 

[markr6]

I suppose it depends on what one considers "storage". To me, it means I likely won't be using that battery for a year or more. In that case, storing at 50% (3.75v) makes a lot of sense.

Charging to 4.1v is for "I don't use this light much, or I probably won't use it for a few weeks." I get about 90% capacity, but it's much easier on the cells. For me, a good compromise.

Charging to 4.2v is for "I use this light a lot, or I need maximum run-time when I use it". I mainly just do this for my Zebralights (and their spares when cycling). I figure if I pay $100 for a light with a great boost-driver for long run-times, I want to actually get those run-times.

In the end, it's probably not necessary to coddle your batteries. I have 10-year old laptop cells that were almost always kept fully-charged, and they still have about 75% of their original capacity. IR isn't great, but laptop cells never were high-drain.

I'm suspicious of the often-quoted claim that a fully-charged cell kept at room temperature will lose 20% capacity per year. Maybe it does that the first year, and then much more slowly after that? Or maybe it's a claim that's only valid for older technology?

I agree with all that. I like 4.1-4.2v for almost everything I do. Daily users, weekly, monthly. One a few truly in storage at 3.6v (likely never to be used again)

 

[dealgrabber2002]

how do you guys know when the battery is at 4.1v? My charger doesn't have a display (2014 Nitecore i2). I should charge it fully then put it in a light and run it for 30 sec. or so on HI?

 

[JoeRodge]

how do you guys know when the battery is at 4.1v? My charger doesn't have a display (2014 Nitecore i2). I should charge it fully then put it in a light and run it for 30 sec. or so on HI?

I would consider getting a DMM(Digital Multimeter) to check the voltage. They are very useful to have around the house. You can find a solid, decently accurate one for about 15 bucks.

 

[flatline]

how do you guys know when the battery is at 4.1v? My charger doesn't have a display (2014 Nitecore i2). I should charge it fully then put it in a light and run it for 30 sec. or so on HI?

The charger I use only charges to a little above 4.1v. I find that convenient. I've got another charger that will go to 4.2v, but I don't use it anymore.

--flatline

 

[WalkIntoTheLight]

how do you guys know when the battery is at 4.1v? My charger doesn't have a display (2014 Nitecore i2). I should charge it fully then put it in a light and run it for 30 sec. or so on HI?

I don't think charging it to 4.2v, then draining it to 4.1v, is a good strategy.

Get a charger with a voltage readout, or a charger that allows you to set the max voltage.

If you can't get a new charger, then you can use a DMM to read the battery voltage while it's charging, assuming you can touch the charging terminals. Note that it will read a little high, since it will give you the charging voltage being used, not the resting voltage. But after some experimentation, you'll figure out when to pull the cell to get a resting voltage of 4.10v. It's probably more trouble than it's worth, but it's one way to do it. If nothing else, it will verify that the charger is using a proper CC/CV method. I had one charger that failed this test, so I no longer use it.

 

[dealgrabber2002]

assuming you can touch the charging terminals.

There are some chargers that let you and some don't?

 

[markr6]

There are some chargers that let you and some don't?

You may not be able to reach in. I used some heavy copper wire attached to the probes that was slightly thinner than the DMM probes so I could fit in that slot. But yeah, a charger with a readout is so much nicer.

 

[dealgrabber2002]

You may not be able to reach in. I used some heavy copper wire attached to the probes that was slightly thinner than the DMM probes so I could fit in that slot. But yeah, a charger with a readout is so much nicer.

I thought I was going to get fried. LOL

 

[Modernflame]

I keep all of mine fully charged. Yeah it might take a year off of the lifespan but li-ion tech moves fast enough that I don't mind buying amazing new cells. I do feel a little bad about wasting money like this just for convenience. But I consider it part of the price of "preparedness" insurance. If the alternative involves stockpiling 100 CR123A then I'm pretty sure I'm coming out ahead.

I keep a stash of CR123's because they are my preferred power source for small, one cell lights. Admittedly, one hundred is far more than I need, but then again I'm a hobbyist. Even just twenty dollars spent on primaries could purchase enough preparedness insurance to relieve the burden on your lithium ions.

 

[WalkIntoTheLight]

I keep a stash of CR123's because they are my preferred power source for small, one cell lights. Admittedly, one hundred is far more than I need, but then again I'm a hobbyist. Even just twenty dollars spent on primaries could purchase enough preparedness insurance to relieve the burden on your lithium ions.

Depends where you live, I guess. A 2-pack of CR123's is $24.99 in the stores, here. Total rip-off. Cheaper on-line, sure, but still a rip-off in Canada. Even on-line, CR123's are almost as expensive as buying a quality 18650.

CR123's do have advantages, though, especially in extreme cold. Eneloops and 18650's don't do well below -20C.

 

[markr6]

CR123's do have advantages, though, especially in extreme cold. Eneloops and 18650's don't do well below -20C.

Really the only "car light" that makes sense IMO. I used to keep a 1x18650 in there until I realized it was toast from the temp swings, mainly the heat.

 

[iamlucky13]

Since no one has stuck their neck out, I'll do it. That figure is wrong and depending on storage time between charges and usage, you are risking permanently destroying the cells, property damage, and injury. No matter what charge you leave your Li-ion, there is going to be a steady self-discharge. At 3.6V, a Li-ion cell is effectively left with no capacity, no wiggle room for storage time, and could easily slip below 2.5V over time. If it does, and depending on how long it remains below 2.5V, when placed back on a charger, you are risking catastrophic failure in the form of an explosion, and fire.

If not cycled repeatedly within about 2 weeks, store your Li-ion cells between 3.8V and 3.9V (about half-capacity). This gives plenty of room for self-discharge in storage, and reduces the charge time if you pull them from storage.

Remaining capacity vs. voltage varies a bit between different models, and 3.6V is usually around 30-40% State of Charge (SoC - going off of HKJ's data for a couple different cells). That should provide significant wiggle room unless the battery is already experiencing elevated self-discharge, or is kept in a light with non-trivial standby drain.

3.9V, on the other hand, is up around 70% SoC. The benefit this provides to storage life is relatively small compared to full charge. The chemistries I've seen data for show a step change improvement in capacity loss during storage at around 60% SoC.

Really, though, whatever state of charge (or voltage as a proxy) you choose for storing your batteries at, you should check them periodically to get an idea how quickly they're losing charge, so you can be sure to keep them in a safe voltage range.

 

[WalkIntoTheLight]

CR123's do have advantages, though, especially in extreme cold. Eneloops and 18650's don't do well below -20C.

Really the only "car light" that makes sense IMO. I used to keep a 1x18650 in there until I realized it was toast from the temp swings, mainly the heat.

I prefer a AA light. It can be run off Energizer Lithium primaries, which are around 1.7v, so suitable for all decent AA lights. Good down to -40C.

That way, I can also use it with Eneloops or any other AA.

Some CR123 lights can be run off 18650s, but they're not as easily interchangeable as AA lithium primaries and all other AA chemistries.

 

[Gauss163]

[...] The chemistries I've seen data for show a step change improvement in capacity loss during storage at around 60% SoC.

That study and others were mentioned in a prior thread on this topic (highly recommended for those seriously interested in such matters). There you will find graphs showing degradation dependence on storage temperature and SOC, including the results of float charging.

 

[WalkIntoTheLight]

3.9V, on the other hand, is up around 70% SoC. The benefit this provides to storage life is relatively small compared to full charge. The chemistries I've seen data for show a step change improvement in capacity loss during storage at around 60% SoC.

Not according to this article:

http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

In terms of longevity, the optimal charge voltage is 3.92V/cell. Battery experts believe that this threshold eliminates all voltage-related stresses; going lower may not gain further benefits but induce other symptoms.

 

[Gauss163]

Not according to this article:

http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

In terms of longevity, the optimal charge voltage is 3.92V/cell. Battery experts believe that this threshold eliminates all voltage-related stresses; going lower may not gain further benefits but induce other symptoms.

First, that is talking about charge termination voltage, not storage voltage. Second, Battery "University" is very far from a reliable source on battery science. It is a collection of snippets excerpted from random places from all around the web. Much of it is wrong, misguided, outdated, old wives tales, etc, and (as here) almost all of its claims are unfounded, i.e. lack proper citations to scientific literature (which is why links to it are blacklisted in Wikipedia). Look elsewhere for accurate information on battery science.

 

[WalkIntoTheLight]

Fair points. Personally, I go with 3.75v for storage, which is about 50% for the common high-drain 18650 cells. Though, I doubt 3.9v is a lot worse. It seems the consensus is that most of degradation occurs when cells are kept above 4.1v. And/or stored in warm conditions.