# Battery temperature during charge and discharge



## MattsAwesomeStuff (Aug 10, 2017)

Don't quote me on this, but I think lithium batteries can be discharged almost at the same rate when cold as when warm. Unless you're drag racing or you have a very short range pack, you're nowhere near maxing out your current draw even when cold.

The recharge rate is what's limited.

I'm not sure if there's a danger in charging them when cold, or, if it's just that they will refuse to charge when cold.

When charging it's an easily solveable issue because you have grid power to run a heater, so you might charge a bit slower (due to wasting energy on heat) but everything will be fine.


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## massawe (Jul 27, 2018)

Thanks Matt. That's kind of what I figured, but of course EV manufacturers go to some great lengths for thermal pack management so I didn't want to overlook things.

I've actually tested these batteries in a lab with the guy who designed them, and we pulled and pushed 500A from them and saw only a small amount of heating near the terminals. I can't remember exactly but I believe we ran at this rate for a few minutes. The room we were in was definitely a nice temperature though, so it's more anecdotal evidence than anything. And of course I will probably be charging at more like 30A off my 6.6kW charger.


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## john61ct (Feb 25, 2017)

You can turn LFP into instant scrap charging too cold.

But the cotes only get **that** cold in places I personally would avoid.

Certainly coastal Oregon should rarely be a problem.

Snow bunnies best stick to lead


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## john61ct (Feb 25, 2017)

http://tnttt.com/viewtopic.php?p=1245996#p1245996


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## Duncan (Dec 8, 2008)

john61ct said:


> You can turn LFP into instant scrap charging too cold.
> 
> But the cotes only get **that** cold in places I personally would avoid.
> 
> ...


This is why the Tesla is the most popular car in that semi tropical paradise called Norway


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## john61ct (Feb 25, 2017)

Tesla's cell chemistry has nothing to do with LFP.

And believe me, the millions spent on engineering their "failsafe" Temp Management Systems is well spent and hard for DIYers to replicate for mobile living space House bank usage.

Any EV's range is cut to a tiny fraction in arctic temps, have a very hard time warming up, and charging is drastically slowed down. 

In the recent cold snap many Tesla owners couldn't even get into their frozen cars.


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## Duncan (Dec 8, 2008)

john61ct said:


> Tesla's cell chemistry has nothing to do with LFP.
> 
> And believe me, the millions spent on engineering their "failsafe" Temp Management Systems is well spent and hard for DIYers to replicate for mobile living space House bank usage.
> 
> ...


You say that but again Norway is one of the places with the most EV's
I think you have been conned by the anti EV lot


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## Hollie Maea (Dec 9, 2009)

Duncan said:


> This is why the Tesla is the most popular car in that semi tropical paradise called Norway


Tesla heats their batteries before charging if they are below freezing.

Charge your Lithium battery below freezing and you WILL destroy it.


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## MattsAwesomeStuff (Aug 10, 2017)

Hollie Maea said:


> Tesla heats their batteries before charging if they are below freezing.


Makes sense regardless because otherwise they'd charge too slowly.



> Charge your Lithium battery below freezing and you WILL destroy it.


If you wouldn't mind... source?


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## Hollie Maea (Dec 9, 2009)

MattsAwesomeStuff said:


> If you wouldn't mind... source?


Well the short answer is "any Lithium battery data sheet" but here is an article that mentions some details about the problem with sub freezing charging:


https://batteryuniversity.com/learn/article/charging_at_high_and_low_temperatures


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## MattsAwesomeStuff (Aug 10, 2017)

Hollie Maea said:


> https://batteryuniversity.com/learn/article/charging_at_high_and_low_temperatures


So, that article is from 2011.

And, IIRC Battery University has bad enough misinformation that it's been disallowed as a valid source on Wikipedia. I don't know whether that applies to this article or not.

The article makes no mention (I only skimmed) of LiFe batteries which were more common back when it was written.

It says that it's okay to charge lithium at a 50-hour rate when cold, and, that charging them generates heat.

I just ask because I've thrown some 18650s into Christmas Light displays outdoors and left them on and out overnight, in -25'C conditions, with no low-voltage protection, let them literally run themselves down to 0v, then slapped them in the charger immediately in the morning at 1A rate (0.5C), and continued to repeat this cycle for the whole Christmas season.

At the end of the season I saw about a 5% decline in battery capacity from their tested capacity at the start of the season. And they were old and used to begin with.

I kind of suspect that the capacity decline is due to discharging flat to 0v, not really the cold at all, as it's about in line with expectations from doing that.

So, while it's a small sample size, I haven't seen evidence that lithium ion batteries are ruined immediately if you charge when cold once.


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## boekel (Nov 10, 2010)

'tesla' batteries:

https://www.batteryspace.com/prod-specs/NCR18650B.pdf

lots of LiFePO4 batteries: don't charge below 5 degrees C

Winston LiFeYPO4: allowed to charge from -45 degrees C


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## john61ct (Feb 25, 2017)

Duncan said:


> You say that but again Norway is one of the places with the most EV's
> 
> I think you have been conned by the anti EV lot


That is true, have family in Norway so not news to me.

Does not change the facts I have been stating, would be foolish for people to buy into new/high tech without knowing those facts.

I am 100% pro-EV, in fact believe no other private automobiles should be legal.

So maybe address the facts you think you might be disputing instead of creating false "us vs them" ad-hominem /genetic*fallacy arguments that are completely irrelevant.


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## john61ct (Feb 25, 2017)

MattsAwesomeStuff said:


> If you wouldn't mind... source?


Like asking for a source on "water is wet".

Do your own basic research, that is one of the first things you will come across.

And if you know so little about a topic, maybe stop pretending / believing you should act as if you know a lot? Dunning—Kruger affects us all. . .

Going down to dead flat is also instant-death, investment is gone.

And each of the dozens of LI chemistries has different characteristics.

LFP is the only one worth considering for House bank storage in a mobile context.


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## john61ct (Feb 25, 2017)

boekel said:


> Winston LiFeYPO4: allowed to charge from -45 degrees C


So he claims, have not seen verification by a source I trust.

If you test it out, please post the results.


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## john61ct (Feb 25, 2017)

MattsAwesomeStuff said:


> lithium ion batteries are ruined immediately if you charge when cold once.


 Has anyone worded their claim that way?

LFP specifically is what is being discussed, not the dozens of other chemistries included in the LI umbrella.

Temperature of the core is relevant, not ambient.

Current rate is relevant.

But the statement

"LFP batts should not be charged when below freezing"

is not disputable.


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## bilbo (Oct 31, 2017)

boekel said:


> 'tesla' batteries:
> 
> https://www.batteryspace.com/prod-specs/NCR18650B.pdf
> 
> ...


I have owned Winston batteries for years. They have performed flawlessly in Canada (i.e. cold) and I would not and have not charged them below 0. The  Winston battery operators manual on pg 15 states continuous and instant charging 0/75ºC. I have seen brochures stating the low charging temperatures but they were probably a translation issue.

Charging below 0 will have a negative impact on the battery. The magnitude of the harm is almost certainly a function of temperature, duration and charge rate.


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## john61ct (Feb 25, 2017)

bilbo said:


> I have seen brochures stating the low charging temperatures but they were probably a translation issue.


I think you're being generous to Mr Chung there


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## Frank (Dec 6, 2008)

As far as I know discharge in cold temps is not an issue, and most people charge as soon as they get home i.e. the pack is probably already warm from driving (discharge) and charging keeps it warm enough.

That said I have installed low-wattage reptile heaters on some of my racing packs (high discharges are easier at higher temps) and external heaters should be fairly easy to implement.


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## IamIan (Mar 29, 2009)

massawe said:


> I am wondering if many DIY'ers are designing in ways to heat and cool the batteries? I live in Oregon, and my biggest concern is probably that I may end up charging batteries during the night when the temperature is below freezing.
> 
> Similarly, I will probably be starting in the morning with a very cold pack.
> 
> ...



I use A123 'flavor' LiFepo4 cells.


Attached are the OEM published specs/recommendations (for rate vs temp s SoC):
Note#1> They don't treat it as a binary .. all max rates at this temp .. and then 1 degree colder zero .. there is a transition of reducing performance .. ie slower charging , slower discharging , more resistance , less power , less capacity , etc.

Note#2> The attached Amps rates is based on a 20Ah cell .. so 200A in that case is a 10C rate .. for a equal performing but 200Ah cell, the same 10C rate would be 2000Amps .. I would also treat those as 'maximums' , and better to be conservative and go less.

---

Also attached is the effects of a colder cell on it's 'IR' effect .. effectively more resistance / less available power / etc at colder temps.

---

Also note .. colder temps also reduce effective capacity .. This not only reduces one's 'range' .. but it also has a compounding effect on the 'effective' C-Rate a given amp rate is treating the cells.

IE when a cell at 20Ah of capacity when warm temps .. 200Amps rate is a 10C rate .. and .. when same 20Ah battery is very cold and dips down to effectively a 15Ah of capacity then a 10C rate is only 150Amps .. trying to still push it at 200Amps when it is that cold is effectively like pushign it at a harder ~13C rate .. this effect is already taken into account in the temperature OEM rate charts.

---

As for what I do .. I 1st , had a thin PTC heating pad to do some targeted heating of battery in winter .. and I just accepted and dealt with reduced usable power / capacity / etc.

I am building a new battery pack that will be in a very well thermally insulated box .. which will significantly reduce the amount of energy needed to regulate battery temperature .. to ether keep it cooler in summer , or keep it warmer in winter .. and I will be adding a small 1k BTU heat pump (dedicated for the battery) for active heating (in winter) / cooling (in summer) beyond ambient air temperatures , still keeping the thin PTC pad for winter .. Thanks to Panasonic Vacuum Insulated Panels (sold at DigiKey) allot of insulation value doesn't need to eat allot of my space ([email protected] thick, [email protected] thick).


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## john61ct (Feb 25, 2017)

Yes although discharge at low temps is much slower, the spec is much lower than with charging and afaik there isn't a danger issue.

Any quality maker will publish the details in a data sheet.


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## jonescg (Nov 3, 2010)

Perhaps the original poster was keen to know whether or not DIY folks are building cooling / heating systems into their battery packs?

If so, then yes, a few of us are incorporating a liquid coolant loop so that cells can be kept fairly close to 25'C at all times. Coming up with a reliable system which keeps things waterproof, and electrically isolated is the challenge.


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## MattsAwesomeStuff (Aug 10, 2017)

john61ct said:


> Like asking for a source on "water is wet".


Then it should be really really easy for you to provide a thorough source on a polite request and not be a jackass and talk down to people about it.



> And if you know so little about a topic, maybe stop pretending / believing you should act as if you know a lot?


You know, I don't think I'm going to take social coaching from someone who treats people like you do.

To your point, that I know "so little" about, was my summary I posted above inaccurate? Nope.

To your point, that I should "stop pretending as if I know a lot", perhaps you should explore your reading comprehension before snapping at people. Did you not see me preface my entire post with "_Don't quote me on this, but_" and, specifically on charging when cold, me saying "_*I'm not sure if* there's a danger in charging them when cold, or, if it's just that they will refuse to charge when cold._? Because it certainly seems to me like I made it very clear that I was not sure and what followed was a best effort that outlined where my knowledge was limited. Also, it happens to be accurate even then.



> Going down to dead flat is also instant-death, investment is gone.


Utterly and completely false.

It's not great for them, it accelerates them through their life, but it is plainly and observably not instant-death. If nothing else, I demonstrated this by doing it repeatedly for the entire Christmas season, in sub-zero temperatures to boot, and only saw 5% capacity decline.

Further, among the thousands and thousands of lithium ion cells I've tested and restored, I've recovered some hundreds of 18650 cells that were at 0V and when charged and capacity tested repeatedly performed equally as well as their neighbors, to spec.

The critical and irreversible point is when a lithium-ion battery gets reversed-charged more than 15%. That can only happen from being in a series string. However, after letting it sit, that battery will return to 0v, making it impossible to distinguish between 2 different cells that are discharged to 0v or discharged 15% past zero, as they both measure 0v.

That probably leads people to falsely conclude that discharging a lithium ion battery to 0v kills them outright.



> LFP is the only one worth considering for House bank storage in a mobile context.


Oh good, I'm glad you get to make declarative statements that overrule every other person's situation or opinion. Announcing you know everything is a very convincing argument.



> "I haven't seen evidence that lithium ion batteries are ruined immediately if you charge when cold once." Has anyone worded their claim that way?


Are you capable of reading what you yourself wrote?

"You can turn LFP into *instant scrap* charging too cold."

Hollie Maea also said, referring to Tesla batteries: "Charge your Lithium battery below freezing and you WILL destroy it", and implying that's why Teslas have battery heaters.



> LFP specifically is what is being discussed, not the dozens of other chemistries included in the LI umbrella.


No... read again, the post I was replying to, by Hollie Maea, was specifically referring to Tesla batteries.



> Temperature of the core is relevant, not ambient.


You're right.

So when I leave some LED lights on overnight, exposed except for a cardboard box in -20'c weather, and they're drained to 0v after about 4 hours and I don't bring them back inside until like, 12 hours later in the morning... 

... your argument is that my observations are false, because in 8 hours the batteries haven't yet had sufficient time to reach ambient temperature?



> Current rate is relevant.


I told you right in the post you're quoting, 1A, 0.5C.

...

Jesus dude you're so angry and wanting to tear down and attack people who were having a civil conversation that you're making a fool of yourself here.

Even if someone's completely wrong, there's no reason to be so rude about it.

Chill out, go find something happier to do if you can't have a discussion without getting angry.


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## john61ct (Feb 25, 2017)

I am in no way angry, but you continue to spread misinformation.

There is very little that can be said about LI as a label. This thread is about LiFePO4.

Going to absolute 0.00V can indeed instantly lead to a 100% useless bank. Not reduced capacity, not reduced lifetime but only good for recycling for its elements.

Same with charging too high a rate when core temp is too low.

These are hard facts, and pretending otherwise serves no constructive purpose.

Now sure, most people do not live in conditions where that will happen, and it is easy and cheap to automate the necessary protections against those conditions.

I am a huge fan of the technology, not saying anything against it by ensuring people understand the risk factors compared to old-school lead.

And since a big quality bank is an investment of many thousands, even if cycle life was reduced to say 800, given the fact their potential in gentle House use may be many decades from 10-20000, my focus is on optimizing longevity, not trying to save a few hundred on protecting the bank.

Again, we are not talking about "lithium ion" in general, nothing related to the chemistries used by Tesla nor any other production EV I've heard of

and anecdotal evidence about mildly cold weather has nothing to do with my statements of facts universally known by anyone doing even the most basic googling about LFP's care protocols.

If my tone is a bit abrupt, I'm not being diplomatic, sorry about that, but I am not trying to get personal in any way, just preventing misinformation that could result in people destroying their very expensive new bank, or making expensive design errors.

Sure with a small bank say 200Ah or under a grand, experiment away and report the results.


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## MattsAwesomeStuff (Aug 10, 2017)

john61ct said:


> but you continue to spread misinformation.


I don't think anything I've said in this thread has been false.



> This thread is about LiFePO4.


This thread is about wherever the discussion goes.

Again, do you have issues with reading comprehension? You don't get to dictate that because the first post asked specific questions about a specific chemistry, that all following items discussed must only refer to that specific chemistry even when clearly stated that they're not. Nor can you then say that comments made about other chemistries are false because they're not referring to the original one.



> These are hard facts, and pretending otherwise serves no constructive purpose.


No one's "pretending" anything. People are having a discussion, and you're apparently having trouble following along but at the same time criticizing people and telling them how to behave.



> Again, we are not talking about "lithium ion" in general, nothing related to the chemistries used by Tesla nor any other production EV I've heard of


"Were not talking about this thing that people are talking about".

If we're talking about carburetors, and the conversation shifts to some contrasting details about fuel injectors, it's absurd of you to say "THAT'S NOT HOW CARBURETORS WORK!", of course not, that's how fuel injectors work, that's why they got mentioned. "YOU'RE WRONG ABOUT HOW FUEL INJECTORS WORK BECAUSE THIS CONVERSATION IS ABOUT CARBURETORS!"

Are you a robot? Do you not understand what a discussion is?



> and anecdotal evidence about mildly cold weather


... -20'c is "mildly cold"?

Also, I was clearly not talking about LFPs.



> I am not trying to get personal in any way


Mhm, "This thing I'm clearly doing, I'm not doing it."

"if you know so little about a topic, maybe stop pretending / believing you should act as if you know a lot?" <-- You wouldn't define that as a "personal" comment?

"So maybe address the facts you think you might be disputing instead of.." <-- Telling someone how to behave isn't "personal" to you?

I think both of those are literally you making a discussion as personal as possible. You're attacking the person making the comments instead of the thing they said you disagree with. And then you're disagreeing with what people said without apparently even reading it and seeing what it's talking about.



> just preventing misinformation that could result in people destroying their very expensive new bank, or making expensive design errors.


Just preventing something that's not happening, by attacking people you don't like, for things they didn't say, about things that weren't being talked about?

The amount of backpedaling going on here...


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## john61ct (Feb 25, 2017)

I'll stop for now, think my point is clear, and I'm not motivated to press for any further clarity on whatever your point might have been.

But yes, discussion of the very different characteristics of each chemistry **should** be segregated to avoid confusion, and members should stop using "lithium ion" as if it designates any one specific chemistry.

If your comments at any point were intended to refer to a chemistry other than LFP, I missed that transition, did not notice whether you specified you were discussing e.g. NMC or LCO or what.

I have no idea about those chemistry's tolerance of charging in arctic conditions, and do not consider them relevant to the thread's discussion.


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## massawe (Jul 27, 2018)

I feel like this thread has given me a pretty good idea of where folks stand. To me it sounds like I have two options:

1) Don't include thermal management, and just be careful when I charge. Perhaps charging after a drive is ok if the batteries are already warm. Perhaps it's better to use a slower 120V charger when in doubt? Probably I could incorporate a gate into my charging system to make sure it never charges when the cells are cold.

2) Include a thermal management system and charge whenever I feel like it.

If I go with option (2) however, I think there are still two options:

a) Include a heating element like a heating pad or nichrome wire to heat the batteries, but don't include a cooling option.

b) Use a fluid heat transfer system that can both heat (electrically, and perhaps from my water cooled motor when I'm driving) and cool (by passing through the radiator).

To me (a) seems much simpler, especially since my batteries will most likely be split up in different sections of the vehicle (I have 60kWh pack). I don't really like the idea of running coolant lines all over the vehicle.

The best way to find out how much they heat up may just be to test it out. 

My plan now is actually to mount the motor and the minimal set of components, then put the seats down and build a simple wooden structure to hold all the batteries. Then connect it up and make sure that things work before going through all the effort of building out the battery compartments. Since my equipment is mostly used (or has been sitting for a few years before I bought it), and since I already have a motor adapter and mount, I think this should be a fairly simple detour on my build and I may learn some valuable things from this test run.

Of course what I won't learn even with this setup is how charging when cold will affect the batteries, so I appreciate everyones input.

On another note, sometimes the internet is the same as a being stuck in traffic: when you can't see someones face or hear their voice intonations, it's easy to make generalizations and just assume that they are purposefully trying to screw you over, and then get unreasonable upset about things. Whereas if you can hear their voice and see their face it's just so much easier to communicate and to see where someones coming from. Not sure what the solution is, just an observation.


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## MattsAwesomeStuff (Aug 10, 2017)

> Perhaps it's better to use a slower 120V charger when in doubt?


It would have to be really slow. I think one of the sources said that you'd have to charge at the 1/50C rate. Meaning, whatever rate would charge them in 50-hours. 

I think you'll probably want liquid cooling eventually, might be worth it to just plumb a heat/cool loop. It's not that much extra work. You need electrical wires, so now you'll add plumbing hoses along similar paths.



> Probably I could incorporate a gate into my charging system to make sure it never charges when the cells are cold.


That's a good idea regardless.

...

I wonder how much LiFeP04's heat up when used. I wonder if, if they're cold, you could just do some kind of max burn on them (toggle in a big ambient heater as a resistive load) before recharging. Even occasionally cycling them into discharge every time they get too cold.

I suppose if you end up below the break-even temperature, you'd drain your batteries dead, but, otherwise just, maybe 15 seconds at a time put a heavy load on the batteries so they heat up again.


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## john61ct (Feb 25, 2017)

Heat is the enemy of longevity.

Internally generated most of all.

Those little embedded silicon pads / wraps are cheap as chips even custom ordered.


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## Yabert (Feb 7, 2010)

massawe said:


> a) Include a heating element like a heating pad or nichrome wire to heat the batteries, but don't include a cooling option.


I use a wire heater in my Smart since 10 years now with success. It's a small 220w unit of 30 feets long with a 10$ thermostat.
Temperature here are around -30°C (-22F) to +35°C (95F) year long and my battery can stay at +20°C (68F) winter long and never go over 35°C (95F) during summer. No cooling.
Heat a battery during winter is really important.

Of course, it have a little bit of foam to insulate the battery box and this one help to maintain temperature in winter and keep heat away during summer.
It's not rare that the exterior temperature is 5°C higher than inside the battery during summer because the temperature is closer to the temperature reach during the night.
The important difference between you and me can be the 16 kWh vs 60 kWh battery. You will be on the road far longer than me and this can cause the battery to heat a bit more.
On the other way, I discharge at around 0.8C (10-15 kw) and you should discharge below this rating.


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## massawe (Jul 27, 2018)

Yabert said:


> my battery can stay at +20°C (68F) winter long and never go over 35°C (95F) during summer. No cooling.
> Heat a battery during winter is really important.


Does this mean you are maintaining the battery temperature at +20C even when you aren't charging/driving? I've read some disturbing things about battery storage temperature, but I am tempted to not worry about this, since my batteries are 6 years old and are still showing slightly above their rated capacity even.



MattsAwesomeStuff said:


> I think you'll probably want liquid cooling eventually, might be worth it to just plumb a heat/cool loop. It's not that much extra work. You need electrical wires, so now you'll add plumbing hoses along similar paths.


Certainly this is probably the 'best' solution. I think the biggest challenge on my build is going to be finding places for all these batteries though. It's truly a boatload. I may have to put a column where the center console goes, maybe hide some under the seats, etc, so it could actually get tricky running hoses, whereas wires are easy (the main power wires are not easy, but small heater wires are). I also wonder, if batteries create so much heat, why do I have to waste half of my Chevy Volt range just to get the slightest bit of warmth in the car? I would think if these batteries were giving off significant heat then that could be used for heating the cabin, no? Obviously I'm missing something here.


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## Duncan (Dec 8, 2008)

Hi massawe

Here (Southland) the idea of cooling my batteries is moot - they simply never get up to those temperatures
I use the batteries to cool my controller

Heating is much more likely to be needed!


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## john61ct (Feb 25, 2017)

Yes cooling is required in only occasional extremes for most setups.

Commercial designs require it for safety, liability, whereas home made DIY we accept Darwin's consequences, make do with safety cutoffs.

Longevity as a goal does not justify the expense.


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## brian_ (Feb 7, 2017)

massawe said:


> I also wonder, if batteries create so much heat, why do I have to waste half of my Chevy Volt range just to get the slightest bit of warmth in the car? I would think if these batteries were giving off significant heat then that could be used for heating the cabin, no? Obviously I'm missing something here.


Operating batteries produce some heat, but on average while driving nothing like the kilowatts needed to heat a car in serious winter conditions. Production EVs with liquid cooling do use excess battery heat for the interior, but waste heat from the controller and motor are probably more significant.


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## john61ct (Feb 25, 2017)

IOW the two have little to do with each other. The energy required to maintain cabin comfort is huge compared to that wasted in the battery chemical reactions.

The need to protect the bank from waste heat is critical to safety and its longevity.

But is only likely an issue when ambient temps are already very high.


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## Yabert (Feb 7, 2010)

massawe said:


> Does this mean you are maintaining the battery temperature at +20C even when you aren't charging/driving?


Yes. All winter long.
Well, except when I know that I will not take my car for a long period of time (more than 3-4 days). 
At those moments the battery temperature can drop at -30°C, after many hours, and I have to start the battery heater fews hours before I drive.


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