# Battery storage in winter



## mk4gti (May 6, 2011)

Not planning on driving my EV this winter (for various reasons). Need to know if I should bring the cells indoors? It gets to -30 here.

The batteries are calb blues 130AH and they are currently installed in a semi insulated battery rack.


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## Ziggythewiz (May 16, 2010)

I certainly would. Cold temps are supposed to be good for reducing degradation, but that is thought to be nearly nil for LiFePO4 anyway, and there has to be some point where cold becomes too cold.

Insulation is irrelevant as given time they will reach ambient anyway.


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## dtbaker (Jan 5, 2008)

mk4gti said:


> Not planning on driving my EV this winter (for various reasons). Need to know if I should bring the cells indoors? It gets to -30 here.
> 
> The batteries are calb blues 130AH and they are currently installed in a semi insulated battery rack.



cold storage is not supposed to hurt them, but do NOT charge if pack is below freezing.


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## dougingraham (Jul 26, 2011)

mk4gti said:


> Not planning on driving my EV this winter (for various reasons). Need to know if I should bring the cells indoors? It gets to -30 here.


Run the pack down about half way and disconnect the battery from all loads. Thats all there is to it. Cold, at least reasonable cold, say down to -40 should not harm the cells. There is going to be a point at which elements of the electrolyte will freeze but that is colder. Probably closer to -100C.


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## TEV (Nov 25, 2011)

From the Calb SE series manual :

Charging: 0 to 45 Celsius 32 to 113 F
Discharging: -20 to 55 Celsius -4 to 131 F
Storage: -20 to 45 Celsius. -4 to 113 F


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## TEV (Nov 25, 2011)

Also disconnect everything including the BMS from the cells


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## batterytang (Nov 17, 2011)

mk4gti said:


> Not planning on driving my EV this winter (for various reasons). Need to know if I should bring the cells indoors? It gets to -30 here.
> 
> -20°C is OK for storage.


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## EVfun (Mar 14, 2010)

batterytang said:


> Of cause you need to bring battery pack indoor.
> 
> Below ZERO celsius degree battery may be damaged if the electrolyte is water-based liquid.. As I know almost all Plastic prismatic LiFePO4 battery belongs to this type, Sinopoly, CALB, GBS etc.


LiFePO4 cells do NOT have a water based electrolyte. They used a solvent based electrolyte. Here is an interesting manufacturer link to some available electrolyte solutions. I recommend using the manufacturers recommendations for storage temperatures, and storing them at 40% to 60% state of charge (most manufactures ship cells in that range.) I would discourage charging below freezing as there seems to be an increased risk of plating due to reduced conductivity.


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## batterytang (Nov 17, 2011)

EVfun said:


> LiFePO4 cells do NOT have a water based electrolyte. They used a solvent based electrolyte. Here is an interesting manufacturer link to some available electrolyte solutions. I recommend using the manufacturers recommendations for storage temperatures, and storing them at 40% to 60% state of charge (most manufactures ship cells in that range.) I would discourage charging below freezing as there seems to be an increased risk of plating due to reduced conductivity.


Yes, you are right, electrolyte can accept -20°C, sorry for the mislead.


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## onegreenev (May 18, 2012)

If you were planning on just leaving them unprotected outdoors then I'd say bring them in. A shed or garage will do just fine even in the coldest areas.


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## Sunking (Aug 10, 2009)

dougingraham said:


> Run the pack down about half way and disconnect the battery from all loads.


OK maybe a silly question but why discharge them to 50% DOD? Isn't the cold just going to take them down further?


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## onegreenev (May 18, 2012)

It's actually one of those misconceptions that get changed into this is what you must do because the cells are shipped pretty much at half charge. So it must follow that if you ship that way there is a reason so it is assumed that the cells sit for some time before being shipped and therefore you must drain yours if you let yours sit too for any length of time. 

Hogwash. I have cells at full charge that have sat for over a year without trouble and cells that have sat nearly drained for the same time without issues. 

This is how myths get started.


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## Ziggythewiz (May 16, 2010)

It's a fact that batteries are damaged more at the SOC extremes than in the middle.


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## onegreenev (May 18, 2012)

Where is the supporting evidence? It is a known with lead acid but not with LiFePO4 cell chemistry. Others will tout claims but no real supporting evidence suggests that. It is known that even the makers of the follow old outdated lead acid information. The thinking is that if it happens to those it must happen to these. There is just no supporting evidence.


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## Ziggythewiz (May 16, 2010)

There's little data for LiFePO4, because it's too new. There is decades of data for other forms of lithium batteries, which all say extreme SOCs are bad. There's no reason to conclude that LiFePO4 has nothing in common with every other lithium battery. In the absence of better data, it's rational to follow what you have.


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## EVfun (Mar 14, 2010)

The cold won't change the SOC of the cells. It will change the rate you can get it out, but that is unimportant in storage. 

For LiFePO4 cells I've seen no evidence showing an impact on life based on SOC during storage, at least between 5% and 95% SOC. Since the manufacturers seem to consistently choose a SOC around 50% for shipping around the world I choose to do the same when storing for months. It is known to be a good practice based on millions of amp-hours worth of battery storage experience by the manufacturers.


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## cpct (May 31, 2012)

From what I read, storing at high SOC would be bad because prolonged high cell voltages tend to break down the electrolyte. I assume this means storing at e.g. +4 V.
Following that reasoning, you would want the highest SOC that is outside those voltages. Then, at a minor self-discharge, it would take the longest possible amount of time before the cell becomes "undervolted".


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## EVfun (Mar 14, 2010)

Based on open circuit voltage I have observed no self discharge is cells stored for 2.5 years. They where stored as received from Thunder Sky back in 2010 and this fall still read 3.29 volts and 3.30 volts. At that time I charged and discharged them, along with 2 others that have seen some use, and got a full 60 amp hours from the cells easily. I recharged the 4 cells to about the 50% mark continue to store them in my unheated (or sometimes slightly heated when I want to work) garage.


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## dougingraham (Jul 26, 2011)

Sunking said:


> OK maybe a silly question but why discharge them to 50% DOD? Isn't the cold just going to take them down further?


Within reason all that cold does is lower the voltage under load. It does not change the state of charge. Because of the electrolyte composition you are probably safe with storage at temps approaching -100C. I would be more concerned with physical damage due to different rates of expansion of the various materials used. An example would be the plastic case becoming brittle due to the extreme cold and splitting. The vendors seem to indicate storage down to around -40C.

My own testing with the GBS 100AH cells shows that storage for 6 months at full charge (resting @ 3.45 volts) and at a 50% SOC (resting at 3.330 volts) showed no change in capacity. An empty cell, discharged to 2.5 volts (resting at 2.7 volts) lost a small amount capacity when stored 6 months. It wasn't much but it was measurable.


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## mk4gti (May 6, 2011)

I'd like to thank everyone for the responses.

I spent the few hours required to disconnect everything and brought the batteries inside. I figured with what they cost, I better protect the "investment".


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## corbin (Apr 6, 2010)

EVfun said:


> Based on open circuit voltage I have observed no self discharge is cells stored for 2.5 years. They where stored as received from Thunder Sky back in 2010 and this fall still read 3.29 volts and 3.30 volts. At that time I charged and discharged them, along with 2 others that have seen some use, and got a full 60 amp hours from the cells easily. I recharged the 4 cells to about the 50% mark continue to store them in my unheated (or sometimes slightly heated when I want to work) garage.


That doesn't mean there was no self discharge. The cells could easily have lost a lot of amp-hours while sitting around for 2.5 years, but still be at 3.30 volts. They wouldn't be lower than that until they got really low SOC.

But, what you are saying is that after the cells sat for 2.5 years, and then you charged/discharged them, they still had the original capacity. so, they didn't loose any capacity after sitting for 2.5 years.


corbin


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## mk4gti (May 6, 2011)

For giggles, I measured the open circuit before and after storing in the basement. (0 Celsius to 18 Celsius). The open circuit voltage at 0C was just above 3.1V and after sitting a day in the ambient temperature, climbed up to 3.29V

I know for a fact the the batteries had roughly 25AH taken from them a day before storage, so about 105AH left (without counting the 80% "limits").

Although open voltage can help troubleshoot in some cases, I find it's never a good capacity indicator when comparing to open voltage of lead, for example. My 2c


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## xmbaleaf (Dec 13, 2012)

if you want to storage your battery,there is storage termperature range.please follow that.

by the way,you must charge it every three monthes when you storage it.


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## onegreenev (May 18, 2012)

xmbaleaf said:


> if you want to storage your battery,there is storage termperature range.please follow that.
> 
> by the way,you must charge it every three monthes when you storage it.



Where are you getting that information?


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## xmbaleaf (Dec 13, 2012)

onegreenev said:


> Where are you getting that information?


 
I hope these information will can help you !

i am from baleaf(xiamen)new energy technology co.,ltd,we engaged in assemble/produce Lifepo4 battery packs for electric car/ebike/scooter,telecome system power and portable solar system for home and so on.

any information,you can contact with me by here/message/mail tooo.


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## Jan (Oct 5, 2009)

You only have to check the SOC, or recharge it so now and than if you've attached a (small) load on the lions. Like a BMS. With no load attached there is no known time limit for storage yet.


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## mk4gti (May 6, 2011)

Not worried about recharging them.

Jack was saying he left a few cells for years at a corner in the garage and they kept their charge.

Will keep an eye on them.


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## EVfun (Mar 14, 2010)

xmbaleaf said:


> if you want to storage your battery,there is storage termperature range.please follow that.
> 
> by the way,you must charge it every three monthes when you storage it.


NO. 

You do not have to charge the cells every 3 months, or even once a year. The cells I charged and then discharged after 30 months untouched storage performed as expected for new cells. They took about 30 amp hours to fill (60 amp hour Thunder Sky cells), and put out a little over 60 amp hours on discharge.


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## xmbaleaf (Dec 13, 2012)

EVfun said:


> NO.
> 
> You do not have to charge the cells every 3 months, or even once a year. The cells I charged and then discharged after 30 months untouched storage performed as expected for new cells. They took about 30 amp hours to fill (60 amp hour Thunder Sky cells), and put out a little over 60 amp hours on discharge.


 
if you done it by this following,you will hurt your battery packs lifecycle and the discharging rate.


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## onegreenev (May 18, 2012)

> if you done it by this following,you will hurt your battery packs lifecycle and the discharging rate.


And again where is the testing that proves your claim? 

I have cells that are just fine after sitting for years without being charged or discharged. 

Where do you get this information? 

Pete


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## onegreenev (May 18, 2012)

What is the mechanism that causes damage by not charging every three months. How can you continue to charge a full cell?


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## mk4gti (May 6, 2011)

xmbaleaf said:


> if you done it by this following,you will hurt your battery packs lifecycle and the discharging rate.


I'd love to see the 5 year graph for trickle charge vs charge every 3 months vs leaving cells alone. I have serious doubt these studies have been done.


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## dougingraham (Jul 26, 2011)

xmbaleaf said:


> if you done it by this following,you will hurt your battery packs lifecycle and the discharging rate.


Non LiFePo4 cells could have an issue but charging fully charged LiFePo4 cells does more harm than good.

I have tested self discharge and there just isn't any measurable over a 6 month time span. The variations are at the granularity of the test gear. Now if you have electronics connected to the battery that is an entirely different matter. A BMS board sitting on each cell could be drawing 20ma from that cell which doesn't seem like much but would drain off 14.4AH per month. (Note: I don't know what the typical BMS load is on a cell but a well designed one would be in the 10 microamp or less range.) But the recommendation for storage that was given is to disconnect all electronics from the battery so that is not a concern.

If you don't believe me take several cells and cycle them a few times each to get a base for capacity. Fully charge them and then let them sit a year. Discharge to determine the remaining charge. Guess what? They are all still fully charged.

This happens to also be true with LiMnO2 type pouch cells. These cells seem to be less stable and something happens to cause them to puff if left sitting around fully charged. The only examples of these I have that did not puff from age are some first generation Kokam cells I got in 2004. Topping them up every three months will almost guarantee cell failure.


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## xmbaleaf (Dec 13, 2012)

dougingraham said:


> Non LiFePo4 cells could have an issue but charging fully charged LiFePo4 cells does more harm than good.
> 
> I have tested self discharge and there just isn't any measurable over a 6 month time span. The variations are at the granularity of the test gear. Now if you have electronics connected to the battery that is an entirely different matter. A BMS board sitting on each cell could be drawing 20ma from that cell which doesn't seem like much but would drain off 14.4AH per month. (Note: I don't know what the typical BMS load is on a cell but a well designed one would be in the 10 microamp or less range.) But the recommendation for storage that was given is to disconnect all electronics from the battery so that is not a concern.
> 
> ...


 
I am sorry that maybe i didn't describe clearly.i meant that: you discharge about 50% capacity before you long storage,then you charge every three months by 0.5C current and ensure keep the battery with 40%-60% capacity/electricity. 

the suggestion as per our data sheet from laboratory.


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## GizmoEV (Nov 28, 2009)

xmbaleaf said:


> I am sorry that maybe i didn't describe clearly.i meant that: you discharge about 50% capacity before you long storage,then you charge every three months by 0.5C current and ensure keep the battery with 40%-60% capacity/electricity.
> 
> the suggestion as per our data sheet from laboratory.


Robert,

What people are saying is that what you are saying is not necessary. Several people have tested just leaving cells alone with nothing connected to the terminals and they are fine, even 2.5 years later. Many of us don't completely believe your "data sheet from laboratory" because independent testing doesn't agree with it. Have your laboratory test some cells by giving them some initial cycles and then leave them sitting at various states of charge with nothing hooked up to them. Let them sit for 1 year and then check the SOC by discharge and then capacity test them. You will find that if the cells were good to begin with, they will not have to be charged every 3 months.


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## Ziggythewiz (May 16, 2010)

I think he's assuming a BMS hooked up leeching off the cells (since all manufacturers recommend/require using a BMS). If that were the case you would need an occasional charge to put back what was wasted.


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## xmbaleaf (Dec 13, 2012)

Ziggythewiz said:


> I think he's assuming a BMS hooked up leeching off the cells (since all manufacturers recommend/require using a BMS). If that were the case you would need an occasional charge to put back what was wasted.


this is one of reasons,other reasons is battery cell come with internal resistance too.battery cells will comsume itself when you long store.

i have one customers who buy cells from other supplier,he used the cells on Hologen heated.in the off-season,he storged his battery cells about 4monthes,and he found that the cell voltage drop from 3.2V to 2.8V.
when he used it again,he found that the cells often like this after that.it shortanced the cell lifecycle ,at least he made a decision and he bought cells from us to replace it.


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## onegreenev (May 18, 2012)

LiFePO4 Cells have no mechanism to drain with no load. There is no resistance when disconnected. Lead acid batteries and a few other types of batteries experience this drainage but not LiFePO4 cells and require no charging during storage. It has been proven time and time again. 

You have a customer that is not telling you the truth.


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## xmbaleaf (Dec 13, 2012)

onegreenev said:


> LiFePO4 Cells have no mechanism to drain with no load. There is no resistance when disconnected. Lead acid batteries and a few other types of batteries experience this drainage but not LiFePO4 cells and require no charging during storage. It has been proven time and time again.
> 
> You have a customer that is not telling you the truth.


 
Lifepo4 cells also have internal resistance,although is very small,you can ignore it when it work,but you will find it is big problem when long storage. for example: 3.2V4Ah internal resistance is about 8mΩ,3.2V20Ah internal resistance is about 3mΩ.


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## onegreenev (May 18, 2012)

Really now? I guess then nearly 3 years is not long enough without a charge. So if there is no noticeable change after 3 years then where is this BIG problem? 

Your sources are faulty. Your customers lie and your lab testing sucks. You gotta do better than this. What can we say. We speak from experience. We have the cells in our garages and car ports. Some even exposed to hot and cold cycles in storage with no charges.


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## xmbaleaf (Dec 13, 2012)

onegreenev said:


> Really now? I guess then nearly 3 years is not long enough without a charge. So if there is no noticeable change after 3 years then where is this BIG problem?
> 
> Your sources are faulty. Your customers lie and your lab testing sucks. You gotta do better than this. What can we say. We speak from experience. We have the cells in our garages and car ports. Some even exposed to hot and cold cycles in storage with no charges.


 
this just discussion,be peace and patience.i just supply the date sheet and proved why i suggest that it will be better when you long storage. 
do you believe your experience or the test equipment?please don't guess,i think if you can provide the date sheet ,maybe i will support you too.why not?


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## onegreenev (May 18, 2012)

It will take me a year for a data sheet. I know my batteries and what I have done. I fully support my experience and it is repeatable by anyone. Go ahead and try it. I will do a video of a charge discharge and post the current capacity then charge it up and let it sit for a year. Along the way I will take voltage readings then after the year I will do another capacity test. Then do it again. So it will take at minimum 2 years or more. But hey, I have already done that and the cells are fine.


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## dougingraham (Jul 26, 2011)

xmbaleaf said:


> Lifepo4 cells also have internal resistance,although is very small,you can ignore it when it work,but you will find it is big problem when long storage. for example: 3.2V4Ah internal resistance is about 8mΩ,3.2V20Ah internal resistance is about 3mΩ.


Internal resistance has nothing to do with self discharge. It only affects voltage while the cell is under load.

And to be contrary I have not found self discharge to be a problem in fact I have found just the opposite. Over a six month test period I found no evidence of self discharge with LiFePo4 cells. That is not to say it couldn't happen with your companies cells. It is possible that like NiMH cells elevated temperatures could induce self discharge but it would need to be considerably higher than 90F because the cells I was storing were in my garage and saw temperatures of 10F to 90F and did not self discharge.

As far as we can tell the only mechanism for discharge is external, some sort of load like a BMS or a DC-DC converter that is left connected and turned on all the time.


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## GerhardRP (Nov 17, 2009)

xmbaleaf said:


> this just discussion,be peace and patience.i just supply the date sheet and proved why i suggest that it will be better when you long storage.


Did I miss it? Can you post this data sheet or a pointer too it?
Gerhard


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## onegreenev (May 18, 2012)

Robert,

It has already been shown that the LiFePO4 chemistry has no self discharge. Now if you put a parasitic load on the cell then YES it will. Other chemistries including some other lithium cells may exhibit this behavior. 
It is after all what the other guys want you to believe. They want you to believe so they can sell you BMS. Or to get us to believe so they can sell us a BMS. Works on some folks, not all of us buy the BS.


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## mk4gti (May 6, 2011)

So is it common for folks to have cells sit in storage with BMS still attached? Makes no sense to me!


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## dougingraham (Jul 26, 2011)

mk4gti said:


> So is it common for folks to cells sit in storage with BMS still attached? Makes no sense to me!


The problem is for the kind of BMS that is on little circuit boards that are on each cell you cant easily remove them.

Not driving your EV everyday is what makes no sense to me.


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## onegreenev (May 18, 2012)

No. The comment is about cells self discharging. The myth is BS used to get you to buy BMS systems. If the cell self discharges in storage it gives reason to believe that you will have this issue as well in a car and you will want a BMS to CURE the ills. 

If you keep charging a stored cell you WILL kill it.


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## onegreenev (May 18, 2012)

mk4gti said:


> So is it common for folks to have cells sit in storage with BMS still attached? Makes no sense to me!


No but I bet you will find some folks doing just that.


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## onegreenev (May 18, 2012)

> Not driving your EV everyday is what makes no sense to me.


If you have a fair weather vehicle it will be that way. Like a buggy or Open top roadster. If you have a daily driver it would only make sense if you did not drive much and there are plenty of folks that don't drive anywhere on a daily basis.


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## mk4gti (May 6, 2011)

dougingraham said:


> The problem is for the kind of BMS that is on little circuit boards that are on each cell you cant easily remove them.


Well I use those boards in my application and it took me 15 minutes tops to remove the 13mm cell fasteners on 40 cells.



dougingraham said:


> Not driving your EV everyday is what makes no sense to me.


If that was directed to me:
I happen to live in an area that has very harsh conditions in the winter. Road salt, cold, snow, freezing rain; -40F is pretty common in January. My next build will have better insulation and cabin heat but for now it's a 3 season vehicle.


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## dougingraham (Jul 26, 2011)

mk4gti said:


> Well I use those boards in my application and it took me 15 minutes tops to remove the 13mm cell fasteners on 40 cells.
> 
> 
> If that was directed to me:
> I happen to live in an area that has very harsh conditions in the winter. Road salt, cold, snow, freezing rain; -40F is pretty common in January. My next build will have better insulation and cabin heat but for now it's a 3 season vehicle.


For a lot of people 15 minutes would be too much effort.

And it wasn't directed at anyone <grin>. It was just a statement. I don't have a heater in my EV yet. The coldest day I've driven it was 13F for the high that day and the car was parked outside. And it was a bit sluggish with the batteries that cold. But still easily performed well enough to stay ahead of traffic. The car is so much fun to drive that I didn't mind the cold. I didn't need anything, it was just a drive for fun. I will get a heater in it and then there will be only those days when it gets to -20 or colder that I might not drive it. I have seen -40F a few times in my life and when it is that cold you just shouldn't go out. For those who have not experienced -40F, it is so cold that it hurts to take a deep breath. I understand perfectly why you would be reluctant to drive during that kind of weather conditions.


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## dougingraham (Jul 26, 2011)

This seemed appropriate to this thread so I thought I would mention it.

This week on EVTV Jack mentioned that he had paid to have a CALB CA60 cell frozen to -300F (-184C). When he got it back it was physically undamaged and it worked just fine. He did mention that on the first charge it did an odd stair step rise of the voltage but this didn't impair its function.

I had theorized that around -110C would be the point where I would expect an issue to occur if one would because this is where the electrolyte would probably freeze.

Unless the sun goes out or a LOX tanker breaks open over a car there is little chance of our batteries getting this cold. I don't think I would be worried too much about my batteries if either of those things happened <grin>

Its nice to know that these cells we are using are physically rugged enough to survive this kind of low temperature extreme.


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## Ziggythewiz (May 16, 2010)

Jack does a lot of 1 off experiments, but I'd much rather see the results of test batches frozen then cycled to death along with a control batch at room temp.

Too bad only the manufacturers would have the resources for a proper test.


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## dougingraham (Jul 26, 2011)

Ziggythewiz said:


> Jack does a lot of 1 off experiments, but I'd much rather see the results of test batches frozen then cycled to death along with a control batch at room temp.
> 
> Too bad only the manufacturers would have the resources for a proper test.


I think it is a cool thing to try (pun intended), and it doesn't prove that you wouldn't see failures if you did lots of them but it is very encouraging that taken to such an extreme that nothing bad happened.


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## mk4gti (May 6, 2011)

This is the data I was looking for. I wonder if a lead acid battery would survive the same exercise !

I would love a long term study (not holding my breath!). (edit: I wrote this at the same time as Doug).
It's like over charging a cell; it's likely to survive a .5v overcharge for a small period. If someone over charges every day then the cell's life will be reduced.

I agree with Zig, manufacturers need to do more extreme testing...


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## Ziggythewiz (May 16, 2010)

I bet they do a lot of the testing we'd like to see, they just don't publish much. The CA cells, for example, have even less info on them than the SEs.


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## mk4gti (May 6, 2011)

So when preparing the cells to go back in the car in March, should I re-balance them ? I'm using top balancing / BMS (no BMS debate here please  )


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## Ziggythewiz (May 16, 2010)

That'd be a question for your BMS to answer. Unless it's completely unbalanced your pack more than it can handle balancing I don't see why you'd need to.


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## dougingraham (Jul 26, 2011)

mk4gti said:


> So when preparing the cells to go back in the car in March, should I re-balance them ? I'm using top balancing / BMS (no BMS debate here please  )


Unless there was some kind of load left on them you will find that they are at the same state of charge as when you removed them so if they needed it then they will still need it now and if they didn't need it when you removed them then they won't in March.

If you left anything connected to the cells then I would suggest you balance them.


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