Anyone------can I safely STORE Lifepo4 battery in cold weather

harpo

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I desperately want to convert our small off grid hunting cabin solar system from AGM to LifePO4. However, I am getting conflicting information about these batteries being STORED for months at a time in sub freezing temperatures.

Yes, I know this it is not ideal to store them in cold weather but that is the reality of my situation. It is impractical to remove the batteries, for instance, in December and re-install in May. We have members that use the cabin sometimes in January or even February and they use the lights etc. If I were to remove the batteries as recommended I would soon be told to replace them with the old AGM's.

So, can I store them in very cold weather without hurting them or not? I know they should never be charged at these temperatures and that is not problem with the right BMS. I am strictly/asking about cold storage and potential damage to the cells.

Appreciate any experience anyone might have in this regard or any scientific papers that might address this issue.

I am aware of different heating elements etc. but I am not too thrilled about leaving any "heating" device for months at a time in a location that is not monitored frequently.
 

NOLA_Castle

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Perhaps cover them with thick blanket? and inside the thick box (inside the cabin/camp)?
 

curiouscarbon

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Calendar aging is slower at lower temperature from what I gather online. The intrinsic aging process that degrades capacity happens faster and faster above 35*C. But below 0*C the chemical reaction is slower and therefore it should lose less capacity if STORED at a low temperature.

One user suggested discharging to 3.2V(LFP) and placing cells in cold storage to reduce Calendar Aging.

Oh ya.. and lithium batteries.. Discharge to storage voltage, put them in the refrigerator....

Of course, it’s important to prevent water from condensing into stuff, but other than condensation risk and excessive charging while cold, I think it might be ok.

Please don’t take my word for it, there are some resources for this stuff around online.

If it’s not charging and doesn’t have water on it, then my guess is the LFP cells will not become damaged from the cold. Excessive discharging can always happen, but the cold ought to be ok. I’m just an amateur tho
 

Sojourner1

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How cold? Will the other members understand the limitations of lfp in colder conditions.

Me personally for a group user cabin keep it simple with what you have and what others have been using and abusing. Sometimes old dogs can't be taught new tricks but if money isn't a problem.....

There are enough threads in this section or a simple search of the forum of members that have built in closures for lfp in extremely cold temps with low draw heating pads.
 

Supervstech

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Storage of LFP needs to discharge to 3.2V per cell… storage when connected to charge can be an issue wearing out the cells rapidly.
 

harpo

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Storage of LFP needs to discharge to 3.2V per cell… storage when connected to charge can be an issue wearing out the cells rapidly.
Thank you for the responses so far.
I have done a search both on the internet and here on the forum. There just doesn't seem to be a consensus. Most everyone agrees that 1) never charge or attempt to charge the LifePO4 battery below 32 degrees F. 2) if storing for more than a month the battery should be left at partial charge somewhere between 40-60%.
To clarify more on my situation: 1) The battery will be disconnected from all sources of load AND charge. Therefore, there will be absolutely no load on the battery and solar panels will be disconnected via circuit breaker from the SCC. 2) Temperatures in Northern PA in the winter will vary from a high of 35-40 to a low of normally 0-30 degrees F. with occasional days below zero. 3) the batteries will sit dormmate for at least 3-4 cold weather months.

There is a lengthy thread here on this site talking about cold weather and LifePO4. I have read all 28 pages of that thread and still can't see a consensus on my specific circumstance. Most just say to take your batteries out of the cold environment and indoors during the cold weather/winter. As stated, that is not realistic for my application. Since I am building this battery from raw cells there is no manufacturer to call about this issue and even then there is no consensus. For instance, I contacted Battleborn. They said it was ok to store THEIR battery long term in cold but to FULLY charge it first. Other manufactures (ReLion and Lion Energy) wouldn't say if it would harm their battery or not but recommended a heating element or their own battery with an internal heating element. This will not work because this is a resistive load that will discharge the battery down to nothing eventually because there is no charging going on at all. So, manufacturers of commercial LifePO4 batteries can't agree on this issue.

This would be a good experiment for Andy of the Off Grid Garage but it never gets cold enough in Australia. He'd have to use a freezer and it would take him months to complete. He is the only one I can find that continually does experiments on these batteries made from raw cells just for the sake of finding out how this chemistry reacts to different circumstances.

Hope someone can point me to scientific paper on this subject or an experiment as mentioned above.
 

curiouscarbon

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Hope someone can point me to scientific paper on this subject or an experiment as mentioned above.

1635266931671.png
Tc = temperature of cell during charge
Td = temperature of cell during discharge

have referred to this paper a couple of times. the big table has DR% on the far right which stands for Degradation Rate per cycle of total Ah. the science people put the LiFePO4 cells in a temperature controlled chamber and heated or cooled the cells to specific temperatures for charging and discharging separately. Some trials were done with Tdischarge = Tcharge. they also tested significantly different Td and Tc. Down into the negatives. They test Tc < 0. hope this is of some use, cheers
 

harpo

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Curiouscarbon, thank you for the post. I am however having a bit of a problem drawing conclusions from the table. Is the full research paper available somewhere that would have a written conclusion to this study?
What I am seeing in the table is that temperature as a function of charging and discharging has somewhat of an effect on Cr long term but not greatly and, perhaps, not even significantly from a statistical standpoint. And, this is after 100 cycles! If true, then why are battery manufacturers all saying not to charge LifePO4 below 0 degrees C? It looks like the most you might lose in Cr long term is 10% and not the dire predictions one hears presently about charging below freezing. Actually, according to this table, charging at -5 degrees C is optimal. Can this be right or I am I not reading this correctly?
Furthermore, it appears this study dealt with charging and discharging at different temperatures. Although somewhat helpful, I am concerned about storage at low temps with no discharge or charge being applied.
 

curiouscarbon

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right on, interpreting it definitely is a task

i also concluded that the 0 deg C charging limit is not a hard one if this data is representative of modern LiFePO4 cell formulations.

full paper available https://diysolarforum.com/resources/general-lifepo4-degradation-vs-temperature.172/download

indeed only 100 cycles were done so it cannot represent thousands of cycles

hear you loud and clear about Topic: Cold Storage with No Dicharge or Charge.

this resource might be of some use? https://diysolarforum.com/resources/why-temperature-of-lithium-cells-is-important.223/

•25°C if the battery is cycled regularly
•15°C (or less) if the battery is in storage or used lightly •Loss of capacity increases sharply with battery state of charge
these are the part i focused on in referencing it.

these lead me to thinking of discharge to ~50% and disconnect all loads to prepare for cold storage
 

upnorthandpersonal

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So, it's very difficult to charge a LiFePO4 battery in the cold in the first place due to the internal resistance getting so high. I tried this:


Storing LiFePO4 in cold temperature is actually good since it slows calendar aging:


I store mine in -20C and below without issues. I don't think state of charge even matters much - as long as you're not drawing power/charging.
 

JoeHam

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No scientific papers here but I have stored one in my garage for a winter where it got to single digit Fahrenheit temperatures without any problems that I have noticed.

No load was connected but it was probably at greater then 50% charge.
 

MJSullivan

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I leave my 72v li-ion electric motorcycle in the shed all winter. I leave it at 50% charge and it starts right up in the spring. No need for trickle charge with my setup. AFAIK, at 50% you can leave lithium batteries for a very long time with no harm.
 

harpo

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Thanks to all who have taken the time to respond to my inquiry. I think I am seeing some consensus that cold storage of LifePO4 batteries with no charging or loads connected to the battery would not likely have a negative effect on the long term capacity of the battery.
If anyone comes up with more evidence one way or the other please post. For now I am moving forward on my plan to replace the AGM's with a LifePO4 battery made from raw cells like so many have done here.
 

harpo

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So, it's very difficult to charge a LiFePO4 battery in the cold in the first place due to the internal resistance getting so high. I tried this:


Storing LiFePO4 in cold temperature is actually good since it slows calendar aging:


I store mine in -20C and below without issues. I don't think state of charge even matters much - as long as you're not drawing power/charging.
Thanks for that link from Solarcity. I found that paper very informative.
 

Bob613

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Do you have a spec sheet for your batteries?
For instance, here is an excerpt from the REPT sheet on my cells. Based on this, I am planning on disconnecting everything including the BMS and just let them get cold - they might get as low as -25C.1638157542627.png
 
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