Lithium and winter storage

[jakegw2]

I didn't reply earlier because I still wasn't sure how I would handle this with my lithium batteries. In the end I decided to play it safe and just swapped them for the original AGM batteries. Now that I have all the parts and experience from swapping them the first time it only took me about 45 minutes to replace the batteries and reprogram the charger, solar, and BMS. They were 98% full when I removed them - I forgot to discharge them before removal so they are just going to get stored that way for the winter. The AGMs are just fine for a single overnight with no AC, which is the only type of camping we will be doing before snow sets in and I store it for the winter. When it gets warm I will have another 45 minute chore to swap back to lithium as part of de-winterizing it.

Not ideal. I have thought about just getting a heating pad and putting it on each battery, but in the end decided this was just the easiest and fastest way to deal with the problem.

[ilmor]

Im not removing mine. Im going to place a wired thermometer in the coach, with the remote sensor next to the batteries. When above 32 ill charge them, if needed. I can use the chassis heater if necessary to warm things up.

[jakegw2]

I didn't see charging as much of an issue as I don't see us camping in conditions where the battery never gets a chance to warm up. My bigger concern was the -4 degree floor. It isn't every year that we get down low enough for that to be a problem, but every few years we will get a cold snap with a night or two at -10 or slightly below. There is absolutely no way I want to be crawling through the snow under the van in those temperatures trying to either remove the batteries or jury-rig a heating device. If we were just a little further south so this wasn't a risk I would have kept them in too.

[ilmor]

As I understand it - there's no need to remove and store the batteries if its cold - the concern is only that you should not CHARGE the batteries when its too cold. This is what Pleasure-Way has told me (in writing, confirmed twice).

[avanti]

Originally Posted by ilmor

As I understand it - there's no need to remove and store the batteries if its cold - the concern is only that you should not CHARGE the batteries when its too cold. This is what Pleasure-Way has told me (in writing, confirmed twice).

Unless your batteries are of an exotic chemistry, this is incorrect. Storage of almost all lithium batteries in frigid temperatures will certainly damage them permanently. The critical temperature is much colder than the minimum charge temperature, but it is quite achievable in most of the US.

It is this fact that caused me to start this thread, and that prevents me from switching to lithium.

[booster]

Originally Posted by ilmor

As I understand it - there's no need to remove and store the batteries if its cold - the concern is only that you should not CHARGE the batteries when its too cold. This is what Pleasure-Way has told me (in writing, confirmed twice).

More and more manufacturers are adding that the batteries should not be stored below -4*F now. It was not that way in the beginning of all the lithium restrictions and couple of years ago. Pleasure-way has been lagging behind as the market went to lithium, IMO, and are just now seeming to be doing better. They may soon also go to the no storage below -4*F, but we will see.

[Davydd]

There won't be any damage of lithium batteries available for RV's which are mostly Lithium ion phosphate, LiFePO4, unless the battery internal core gets down to -4º F (-20º C). You shouldn't charge them if below freezing.

[booster]

All of the talk of the lowest temps for charging and storage of the LFP batteries makes me wonder just what the damage curves actually are in regards to temperature.


Very few things in material properties have sharp temp cutoffs, I think, with the possible exception of water which freezes pretty close to 32* but with some small variations.


My point would be that if -4* is the minimum storage spec, how bad is -6* compared to -2*? -10* compared to +4* degrees? Etc. My guess would be it is like many properties that are a more continuously increasing likely hood than on of/off good/bad thing. -4* may just be a balance point of cost, convenience, failure, and maybe even marketing for instance, and same with the charging point of +32*.


I have looked several times, but not exhaustively, and have not found anything I would consider good data on it, so still up in the air to me.

[ilmor]

I see so many opposing views on this I don't know what to believe. Pleasure-Way tells me that they never remove their batteries in their coaches over the winter and they are located in Saskatoon, Canada. Since I have this in writing from them I'm just going to go with it. I also live in the southern US so I'm not as concerned about it as those in the frigid north may be - Ill certainly see nowhere near -4F!

[Davydd]

This is a very good source of information in regard to cold weather for lithium ion batteries. It was written by Fred Ahlgren, engineer, and a longtime Class B RVer who built his DIY Class B about 15 years ago and now has an Advanced RV Class B with lithium batteries. He consults with ARV in developing their lithium ion batteries. ARV has experience dating back to 2014 with custom designed battery banks and drop-in lithium batteries early on. This PDF documents the three systems they offer in Elite Power Solutions, Lithiumwerks Valence batteries and the Volta system now offered by Winnebago and others. Elite was first made aware to RVers by Technomadia in 2012 and I have had them in my ARV since December, 2014. Valence is a drop in profile that I plan on having next. Volta is the 48v package system of batteries, inverter, converter and second alternator. The only revision is this paper is Valence is now LiFePO4 batteries instead of LiFeMgPO4 batteries and I mentioned that in a previous message in this thread.

Advanced RV Lithium Batteries

For the record, I have an 800ah battery bank going on 5 years and two winters I stored outside in the Minnesota winters and still going strong. ARV, a custom builder, has hundreds of its RVs on the road and unlike other upfitters it has a close relationship with all its customers and has direct feedback. Unlike other upfitters it also has developed fail safe measures no one else has installed in battery monitoring and control.

I have no qualms in having lithium batteries in cold weather. As I have said before, I boondocked for a solid week with temperatures always below freezing day and night down to a -5º F and have boondocked two other times in morning temperatures down to -15º F. As I said my first two winters I stored outside in Minnesota winter temperatures that reached more than -20º F. a few times. It is not up in the air for me.

[booster]

Davydd, you missed the point. I never said anything about if they can be used when they are warm enough, like yours were with heaters when stored and charging above the prescribed limits.


What I said was that I wondered just how hard and fast the limits are, and if being close to them is causing some, but not as much damage, and if going under them gets progressively worse. That is what, IMO, is still up in the air.

[avanti]

Originally Posted by booster

Very few things in material properties have sharp temp cutoffs, I think, with the possible exception of water which freezes pretty close to 32* but with some small variations.

Is this correct?

I am not a materials scientist, but my understanding is that nearly all materials have characteristic freezing points. Isn't that what Gibbs free energy curves are all about? It is true that the melting point and the freezing point aren't always exactly the same for a few materials, but this doesn't change the fact that freezing will happen at a very specific temperature.

Am I confused?

[jakegw2]

Davydd - Did the core temperature of your batteries drop into the -10 degree range at these times or was there some sort of heating applied to prevent that from happening? Booster might be onto something here - it could be that there is a time and temperature depth scale that matters. Speculation: perhaps briefly hitting -4 or -10 for a few hours causes some very minimal level of damage (on the order of storing a battery at 99% charge instead of 50%) but hitting -20 degrees ruins the pack.

My thinking so far has been along the lines of what avanti suggests - the -4 degree temperature is the freezing point of some critical material inside the LiFEPO4 batteries and the phase change will destroy their internal structure.

[ilmor]

Originally Posted by jakegw2

Davydd - Did the core temperature of your batteries drop into the -10 degree range at these times or was there some sort of heating applied to prevent that from happening? Booster might be onto something here - it could be that there is a time and temperature depth scale that matters. Speculation: perhaps briefly hitting -4 or -10 for a few hours causes some very minimal level of damage (on the order of storing a battery at 99% charge instead of 50%) but hitting -20 degrees ruins the pack.

My thinking so far has been along the lines of what avanti suggests - the -4 degree temperature is the freezing point of some critical material inside the LiFEPO4 batteries and the phase change will destroy their internal structure.

Now here's an article that says -40 (not -4) is the critical temperature.

https://www.ufo-battery.com/does-col...um-ion-battery

[booster]

Originally Posted by avanti

Is this correct?

I am not a materials scientist, but my understanding is that nearly all materials have characteristic freezing points. Isn't that what Gibbs free energy curves are all about? It is true that the melting point and the freezing point aren't always exactly the same for a few materials, but this doesn't change the fact that freezing will happen at a very specific temperature.

Am I confused?

I can't be certain about pure elements, but most of the stuff that I dealt with, like metals, brazing alloys, etc had a "solidous" and "liquidous" plus the brazing stuff would have a "remelt" temp that was usually higher than either of them. For a metal things like the tensile and bending strengths change over a range, not like a switch, with temperature changes.



A better example of what I was indicating would be a lead acid battery vs temp for charging and damage which gets progressively worse for damage as the temp rises. Same is true with discharge depths, where deeper discharges do more damage than shallow ones. Even things like engine wear vs internal temperature gets progressively worse above the ideal point and also progressively worse below that point, but probably at a different rate.

[booster]

Originally Posted by ilmor

Now here's an article that says -40 (not -4) is the critical temperature.

https://www.ufo-battery.com/does-col...um-ion-battery

It says they freeze at -40*C, not that they don't get damaged or deteriorate faster.



It is easy to find literature and recommendations for the -40* storage as not everybody has gone to it yet, but the trend was started by the high end, high tech, manufacturers so it carries higher credibility for me.

[jakegw2]

The article ilmor links to is very interesting. Not comprehensive, but seems to suggest that the limits are:

32 degrees F for charging
-4 degrees F for discharging
-40 degrees F for storage

If I had known this I would have left my LiFEPO4 batteries installed and just turned off the disconnect to prevent any charge or discharge.

[booster]

This is the internet, so it is likely you can find something to support what you want in most everything, so single articles don't count for much especially when they are a couple of years old and refer, it appears, to older information than that.


This is the first thing that came up for me in a Google search for LFP storage temperature.


https://www.batteryspace.com/prod-specs/9055.pdf


It says storage temp should be at 0*C or the same as the charging temp limit.


It takes a lot of reading and searching to weed through all the information out there as it is very often contradictory. It is always useful to research the author of the article to look for conflicts of interest, experience, sources for the data in the claims. Basically, a research project of your own.


Do I believe that the link here is absolutely correct? Nope, it is just one data point, and is on the fringe of what I have seen other places for the spec.

[@Michael]

Originally Posted by booster

What I said was that I wondered just how hard and fast the limits are, and if being close to them is causing some, but not as much damage, and if going under them gets progressively worse. That is what, IMO, is still up in the air.

I recall the Battleborn guy saying something to the effect that the colder the temp, the lower the acceptable charge/discharge rates. Something to do with how fast the ions can move between poles. He implied that these were not hard limits or strict cutoffs. BB's internal BMS cuts off charging at something like 25F.

I also recall one of the major battery mfg's publishing a temperature derating curve for charge/discharge rates, implying that lower charge rates == lower temps.

[booster]

Here is a quote from a Lithionics battery spec sheet that appears to show it is a sliding scale based on how long the battery is stored, with the temp going up the longer the battery is stored.

Storage Temperature & Humidity Range:
< 1 Month
-4~95°F (-20~35°C), 45~75%RH


< 3 Months
14~86°F (-10~30°C), 45~75%RH


Recommended storage
59~95°F (15~35°C)，45%RH~75％RH