Question About Li-ion Storage

[RichS]

I have recently moved my lights and batteries - all of which run on lithium or li-ion batteries - to the garage. I just moved into a new house we built, and with the number of lights and associated lithium/li-ion batteries I have, I decided to store them in the garage for safety. I keep them in a metal tool cabinet in a couple of the sliding drawers just in case of a battery flame. I know it will probably never happen, but it's just good piece of mind.

Now for the question - it's COLD! so I would say that the garage gets down to the 20s and 30s in the coldest part of the winter. Is it ok to leave all the lights and batteries out here? All winter long?

If so, do I need to do any special maintenance, such as top off the batteries every so often, etc?

Thanks for your help!

-Rich

 

[SilverFox]

Hello Rich,

The cold will not be a problem.

You can discharge the cells a little. This may help the storage conditions. You are shooting for an open circuit resting voltage of around 3.9 volts.

You should see very little self discharge, so all you have to do is to store them. No topping off needed.

Tom

 

[Burgess]

Hey Silverfox, while yer' here . . . .





How are Lithium-Ion cells (specifically AW's 18650's)

affected by Cold during actual USE ?



Let's say (for example) that i get 2 hours of service

on a battery charge at Room Temperature.



What can i expect at 32 degrees F ( 0 degrees Celsius ) ?



Thank you for all your helpful advice !

:thanks::goodjob:
_

 

[Jauno]

IMO, problems arise when water starts freezing so below zero celsius temperature.
We all (?) know how awkards is using mobile phone (with li-ion) in below zero weather. But after 3 winter use of my AW rcr123, 17670 and 18650 i haven´t have any problems in cold weather, although i must say that we don´t have really cold weather in southern part in my country.

But i am li-ion fan, so i also want to know how cold affects li-ion storage. And everything else about li-ions

Pila says temperature range is -20c -> 60c. Is this only operating temp or is it good to storage li-ion as cold as -19c? What about charging in car charger at cold weather.

My thoughts why "flashlight li-ions" perform better than "mobile phone li-ions" in cold:
In flashlights cells are bigger (more capacity) and they are dicharged faster so they don`t "freeze" so easily. Also metal casing of cell and in most cases also flashlight metal body helps, especially when moving from warm temps to cold outside.
Heat is the enemy to the high-power leds, but in cold weather it is li-ions best friend so heat produced by leds also helps.

Experts, please let me know if i´m wrong

 

[SilverFox]

Hello Burgess,

All battery chemistry slows down during cold temperatures. As a result, the voltage under load drops, and you end up with shorter run times.

The RC people have found that their battery packs suffer performance losses at temperatures below around 60 - 70 F. When flying in "cooler" temperatures, efforts are made to preheat the battery packs before use.

At 32 F with a Li-Ion cell, it looks like there is around a 0.25 volt drop under a 1C load, and a reduction in capacity in the 10 - 20% range. At colder temperatures the losses are greater. Each manufacturer has their own mix of chemicals used in the cells, and I would expect each brand of cell, or perhaps each batch of cells to perform a little differently.

Keep in mind that we are talking about bare cells here. There have been reports of protection circuits failing when protected cells are placed in the freezer for storage. The cells were fine, but the protection circuits failed.

Tom

 

[SilverFox]

Hello Jauno,

It is not advised to charge Li-Ion cells in cold temperatures. When charging, you should bring the cells up to room temperature, then charge.

The -20 to 60 C temperature range is for use (or storage). Not for charging.

Tom

 

[RichS]

Hello Rich,

The cold will not be a problem.

You can discharge the cells a little. This may help the storage conditions. You are shooting for an open circuit resting voltage of around 3.9 volts.

You should see very little self discharge, so all you have to do is to store them. No topping off needed.

Tom

Great! Thanks so much for the information on this. It's also good to know that I need to be sure to bring the cells up to room temperature before charging.

I had no idea I would get the master himself to weigh in on this! :twothumbs

 

[witness]

storage of Li Ion batteries (18650)

I understand one should store Li Ion batteries at about 40% charge. Does that mean 40% of the voltage?
AW told me to store the 18650's at 3.8-3.9 volts but how is this 40%. Is that the voltage at which energy density reaches 40%?

 

[Burgess]

Re: storage of Li Ion batteries (18650)

Yep !

Remaining capacity -- not energy density !

 

[witness]

Re: storage of Li Ion batteries (18650)

Yep !

Remaining capacity -- not energy density !

Thanx,
Just out of curiosity how is capacity measured (formula)?

 

[45/70]

Re: storage of Li Ion batteries (18650)

Just out of curiosity how is capacity measured (formula)?

If you are asking how is the capacity estimated by measuring the voltage of a cell, there are several charts/tables around on the Forum, but this is the one I use. Note that the open circuit cell voltage should be measured at least 20 minutes after the cell has been in use/charged, ie. you are measuring the "rested" cell voltage.

4.20 Volts = 100%
4.10 Volts = 90%
4.00 Volts = 80%
3.90 Volts = 60%
3.80 Volts = 40%
3.70 Volts = 20%
3.60 Volts = nearly discharged
3.50 Volts = discharged

There are several of these around with slightly different numbers, but they're all pretty close. Often discussion arises about how accurate these figures are. Just keep in mind that this is only an estimate.

Long ago it was mentioned that due to different methods of assembly, and exact chemical composition and construction materials used by different manufacturers, the estimates around and below 3.80 Volts are less accurate. I find this to also be the case when estimating the capacity of older, or well used cells. These cells, which have a somewhat higher internal resistance, may actually have more capacity remaining than the chart suggests.

Also, these figures are for estimating the capacity of LiCo (ICR) Li-Ion cells, the most common type we use. For LiMn (IMR) and LiNiCo (another form of LiCo/ICR cell) Li-Ion cells, the figures are fairly close, but may be off a bit, again particularly at readings below about 3.80 Volts. And of course, for LiFePO4​ (IFR) Li-Ion cells, the figures do not apply.

Dave

 

[witness]

Re: storage of Li Ion batteries (18650)

Thanx Dave.

 

[witness]

Another question.

When I got a bunch of AW 3100mah 18650s I didn't know any better and fully charged them all so they would be ready to go when needed. I guess I should run them all down to 3.8v as soon as possible?

 

[45/70]

Re: Another question.

It depends on what you mean by "a bunch". Some people keep their cells fully charged all the time. This makes sense, if you use them all the time. On the other hand, if the cells are going to be sitting around unused most of the time, that's different. In the later case it makes more sense to store the cells that are not "in use" in a 40% SOC, and just rotate them with the cells you are using. That's what I do. This means that my cells spend 80% or more of the time degrading at one third the rate (40% SOC, in the Fridge) of the cells that are in use.

If you have 10 cells and 5 lights that use them, and you use all of these lights all the time, it might not make much sense though. As for myself, I have about 40 lights that use Li-Ion cells, and about 130 Li-Ion cells in a dozen or so different sizes. And no, I don't carry more than one light around on my person (plus my modded SL Keymate), and only have 2-3 lights actually in use at home. Add to that, I also have about 20 lights that use NiMh cells. So, for me the storage/rotation method works out quite well, for both my Li-Ion cells, and lights. I use them all, but in essence, only "part time".

EDIT To Add: I wouldn't be in any big hurry to discharge your cells. Just use them in your lights, unless it's going to be months or something before you use them.


Dave

 

[SilverFox]

Re: Another question.

Hello Witness,

A while back I ran across this formula for determining the state of charge of a Li-Ion cell based upon its voltage. This is supposed to be valid for the state of charge range from 30 - 100%.

Once again treat it as an estimate or an educated guess.

SOC% = 100 (0.1966 + square root (0.0387 - 1.4523 * (3.7835 - voltage of the cell) )

Have fun.

Tom

 

[Viking]

Re: Another question.

Hello Witness,

A while back I ran across this formula for determining the state of charge of a Li-Ion cell based upon its voltage. This is supposed to be valid for the state of charge range from 30 - 100%.

Once again treat it as an estimate or an educated guess.

SOC% = 100 (0.1966 + square root (0.0387 - 1.4523 * (3.7835 - voltage of the cell) )

Have fun.

Tom

Can you give an example ?

The numbers makes no sense to me :thinking:

 

[witness]

Re: Another question.

Anyone know why a good charger like the Pila doesn't have a built in voltmeter? I just got Cottonpicker's high current solar charger and it has one. It seems to me that a built in voltmeter would be a necessity with Li Ion batteries.

 

[Viking]

Re: storage of Li Ion batteries (18650)

If you are asking how is the capacity estimated by measuring the voltage of a cell, there are several charts/tables around on the Forum, but this is the one I use. Note that the open circuit cell voltage should be measured at least 20 minutes after the cell has been in use/charged, ie. you are measuring the "rested" cell voltage.

4.20 Volts = 100%
4.10 Volts = 90%
4.00 Volts = 80%
3.90 Volts = 60%
3.80 Volts = 40%
3.70 Volts = 20%
3.60 Volts = nearly discharged
3.50 Volts = discharged

@ 45/70

I know you are a battery "Guru" and have a lot of knowledge.
But are you sure that chart works for newer cells .


I know nothing about it. But I just read this in another tread:

4.2V = 100%
4.1V = about 90%
4.0V = about 80%
3.9V = about 60%
3.8V = about 40%
3.7V = about 20%
3.6V = empty
<3.5V = over-discharged

This is not correct for new AW 2900mAh and AW 3100mAh cells. Or any other Panasonic NCR18650 based cells. They still have around 40% of capacity left at 3.6V OCV.

The new 2900/3100s can be discharged safely down to 2.5V, but the older chemistries can only be discharged to around 2.75V. The discharge curve for the 2900mah NCR is posted here. At 3.6V the cell still has more than 50% of its capacity so you shouldn't start charging at 3.6v.
http://industrial.panasonic.com/www-data/pdf2/ACA4000/ACA4000CE240.pdf
You would notice that the cell only reaches maximum capacity when it's above 60 degrees celsius (or 140 F). Which is why i laugh when people say you shouldn't run a high powered light for too long and let the cells get hot in use or it'll cause explosions Or that once the battery gets above 40 degrees celsius it would explode. Temperatures above 50 degrees will actually net more capacity and the cell can survive way higher temperatures than 60-70 C. However, the only thing is that storing it at high temperatures will increase permanent loss of capacity to above 10% per year.

The quotes are from this tread starting from post 102

http://www.candlepowerforums.com/vb/showthread.php?280909-Ultrafire-18650-3000mA-exploded/page4

 

[witness]

Re: storage of Li Ion batteries (18650)

This is not correct for new AW 2900mAh and AW 3100mAh cells. Or any other Panasonic NCR18650 based cells. They still have around 40% of capacity left at 3.6V OCV.

I don't think that is right. Here is the message I got from Andrew at AW on CPF Marketplace when I asked about storing the 18650 3100ma AW's:

"You can store LiIon batteries at room temp. ( 25 degree C ) at around 40% charge ( about 3.8 - 3.9V ). No need to refrigerate. Expect shelf life is 3 -5 years."

 

[45/70]

Re: storage of Li Ion batteries (18650)

@ 45/70 ......
......are you sure that chart works for newer cells .

Hi Viking. As I said, at voltages around 3.80 Volts and below, the chart can become inaccurate. I also mentioned that with some cells, such as LiNiCo (which is what the Panasonic 2900 and 3100mAh cells are), that the chart can become even more inaccurate.

Still, all that said, the chart gives folks something to at least get an idea of where a cell's remaining capacity stands. And remember, it has never been suggested that these figures are certifiably accurate. That is why there are several of these charts around, with slightly different figures. They are just a general guide for all LiCo cells.

Also, be aware of confusing voltage when a cell is under load, with open circuit cell voltage. The lower a cell is drained, the bigger the difference. This of course, depends somewhat on the current under load, but I've pulled cells out when their voltage was at ~2.75 Volts under load, that read 3.7 Volts OC. In that particular application, the cell was for all practical intents and purposes, discharged.

OT, great name, Viking. My heritage is probably Viking, on my Dad's (R.I.P.) side. I really know nothing about it however. My great, great ...... great Grandfather, came to America from Scotland in the mid 1700's. I do not know how long the family name had been in Scotland at that time, but have been told it is most probably Norse. That's about all I know.

Dave