What would the voltage be for a typical 18650 Li-ion cell at 40% charge, for long term storage, unused, in the refrigerator?
40% is the recommended state for long term storage, correct?
Too, does storage in a freezer stop the aging of Lion primaries as it does with alkaline and carbon?
Very close to stopping it. Most 18650 will be rated for –20C storage (or colder), but not all of them so be careful. Your freezer will get close to –20C.
Always allow time for warming, and condensation to evaporate.
Hi Brian, have a read of Lithium-ion battery safety 101 it will tell you everything you need to know and more.
I usually store my 18650s at 3.8v
Thanks; I read the battery safety thread but missed the storage voltage. I saw it this time through. Duhhh! On me. 
Last I checked my freezer it was –20F, so that’s out. That leaves my refrigerator out in the shop which I keep very close to 32°F
Maybe stored in a sealed container in the fridge cooler compartment, not the freezer i would think.
I store mine at around 50% measured cell capacity as cell voltage can differ between cells.
Anywhere between 40 - 60% is cool :laughing: for long term storage. I use 50% to allow for some self discharge which may be more prevalent in protected cells.
HKJ did some testing on this
Thanks!
If I’m understanding that chart it appears that different brands and models of batteries can have wildly different capacities at a chosen voltage. If I decide to store a battery at 3.7 volts it could be almost dead and others would be fine. That complicates matters doesn’t it?
Mountain sells this charger: http://www.mtnelectronics.com/index.php?route=product/product&path=79&product_id=417
Would it tell me what I need to know for proper storage of the batteries? Or is it just to be a crude representation of capacity and not usable for this*? BTW, I have a DMM to check voltage. Or am I just making more of this than it needs to be?
*Implied in that question is another… is there an easy way to check capacity? Again, am I making more of this than I should?
My problem is that I have far too many batteries and I can’t see leaving them out to degrade rapidly if I don’t need to use them. My experience with Nimh batteries didn’t do so well when moving to Li-ion batteries. These things last close to forever before needing a charge in my normal use, and I use them every night. Before anyone writes something… no, I’m not taking them too low before charging. At least not by DMM. But if that charger (above) actually is accurate it might be a better guide.
I use my MC3000 that discharge the li ion at 3.7 volt for storing purpose.
However the fridge thing make sense IMHO if you have a lot of batteries.
If I have to start worrying about the li ion in the fridge (did someone put oil on them? or added to the salad?), and their humidity/rust, it has to be for some expensive battery.
Today you can buy cells for less than 4€ each, and remember that every year that passes the cells you have in the fridge will still decay, while the ones you can buy should be not only new, but also with improved performances due to constant research.
That charger (VC2) doesn’t have a discharge function, which is the only real way to determine capacity.
It shows how many mAh is put into the cell, which does give a fair guide on healthy newer cells but maybe not so much on older ones.
3.8v should be a fine rested measurement for storage of cells though.
Don’t worry about it too much, you’ll be wanting to replace cells every 3-4 years anyway.
Maybe the Opus BT-C3100 V2.1 would be better for you.
Thanks guys. Looks like I’ll be getting that Opus charger.
Yeah, noobs do stuff that just doesn’t make sense! OK, I’m discussing myself. I didn’t have a clue, but I don’t want to just destroy these batteries either. I simply don’t need so many charged batteries.
I live in an earthquake and fire danger area and I keep all my 18650 and 26650 batteries charged and check them every three months with a static voltage measurement. Batteries are stored in a cool, dark, and dry environment.
I have been following this procedure since 2012 without problems. From my reading and listening to people on lithium ion battery safety and battery efficiency there is no absolute method for storage.
What is needed is an evaluation of battery needs and requirements without regards to the time and external power needed to charge lithium ion batteries.
Old thread…but still relevant and came up in Google today while searching on “Storage of Lithium batteries”
Didn’t HJK say the MC3000 is by far the more versatile charger?
I have one…it most certainly does have a Discharge function and also Refresh, Cycle and many other customizable functions.
Oh, here it is……
Of course the MC3000 is far more versatile . I was refering to the VC2 BrianK linked, not the MC3000 
I store them fully charged at around 16 C.
The temperature is good and requires nothing to keep it there.
Storing them fully charged may not be the officially recommended practice, but that way I can quickly detect in time if any of them have problems (voltage drops significantly instead of just a little over a long period).
Same here. I suppose keeping my Go-bag in the refrigerator might slightly improve their longevity, but I can live with recycling and replacing cells every three or four years. I already have to do that with the alkaline cells.
Most everyone says to store at cool temperatures, but this was on the web months ago:
“Lund Instrument Engineering: July 19 2018. https://www.powerstream.com/Storage.htm:
Cadex’s recommendations are to store below 15° C (59 F) at 40% of full charge…. Our experience is that with cells stored at room temperature for 3 years that the non-recoverable capacity did not decrease, so this is probably manufacturer dependent.”
I am not sure about the wording there, but assume they meant to say they could recover capacity about the same as with the Cadex recommendation? Anyway, after reading that my extra refrigerator space has been dedicated to beer, LOL. But each to his own, do whatever seems right to you.
Calendar aging strongly depends on time, SOC and temperature.
Thank you, docware for the info.
Apparently another factor is manufacturer (chemistry) since they seem to have said they had good experience with their batteries (Panasonic if I remember correctly) after 3 years at room temperature. Some of the information on the web is not dated and we seldom know the latest manufacturing schemes, but we can hope quality is improving with added research. Do you know what years the graphs you posted represent and the battery or batteries tested?
Still, the statement I quoted was removed from their website, so it might not have been totally accurate. I am not trying to argue, but just find cell data to be hit and miss. That is one of the reasons BLF is so useful, so thanks to all who share their analysis of lights and cells.
The study is dated 19.4.2017, cells are Panasonic NCR18650PD. You can read the whole study here :
Calendar aging - page 43 till page 71.
Different chemistry, manufacturer, electrolyte additives, …… may have little bit different results, however the statement from this study is in general valid for all cells : calendar aging strongly depends on time, SOC and temperature.
Thanks for the link, docware, I’ve saved a copy of that 
Yes, thank you. Very informative study.
The graphs you show and the ones on page 69 seem to indicate storage at 10C (50F) and 25C (77F) might be acceptable depending upon ones needs. It is very high temperatures and high SoC that are problematic. Cells stored at 3.7V for 15 years are thought to exhibit a capacity fade of 6% at 10C and not quite 10% at 25C. Maybe this is why Lund Instrument did not find temperature to be a major problem for 3 years. Since I do not intend to store my batteries for 15 years, the beer wins the extra space in my refrigerator, not my batteries.
Stored at 4.1V at 25C they are estimated to lose 16% capacity in 15 years, which is much better than one would think. But it is not inconvenient to store at lower voltage, so that is where I will focus.
Please correct me if my thinking is in error and thanks again for providing the study. It can help anyone can see the impact of various factors on their storage decisions.