# Lead acid batteries in the cold?



## joseph3354 (Apr 2, 2008)

they have to be warm all the time,i have read that people are using waterbed heaters for this purpose.not sure of the safety or effectiveness of that.batteries will lose some capacity even at 50f.not much but may be noticable in an ev.they will warm up in driving because of the draw on them.


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## MrCrabs (Mar 7, 2008)

I have read that lead acid batteries like temperatures that humans like (as a generalization).
I am not sure of the exact reason why they lose capacity when it gets cold, but I do know the water in them can freeze at a certain point, It which case I don't think they would be able to produce electricity.

I am in Buffalo, so am planning on how to deal with the cold. I am thinking I will build insulated battery boxes, and line the boxes with Battery Blankets. http://www.google.com/products?hl=en&q=battery+blanket&um=1&ie=UTF-8

The idea is to use turn the blankets on when plugged into AC power, to warm up the batteries if necessary before charging.
I would also like to have some sort of timer, so that the blankets turn on 1 hr or so before my normal commute so I have full capacity when I leave the house.

During the day, hopefully the insulation will be enough to keep the batteries warm/above freezing.

A fully charged flooded PbA will freeze around -20 F, if it is fully charged but the temp is 30 F then it will act like its 50% DOD (voltage and current will be lower as if it was half way discharged)

Search for "Batteries in the passenger compartment?" in the EVDL forum section, or the EVDL archives, this came up on 4/29


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## JRP3 (Mar 7, 2008)

Batteries are a chemical reaction, and chemical reactions slow down in the cold, hence the reduced capacity.
To get around the freezing problem, as well as to get improved performance and battery life, I'm using Odyssey AGM batteries. More expensive than flooded of course, but if they last as promised they will make that up with longevity.


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## tazdotnet (Apr 9, 2008)

ok to explain why batteries lose power in the cold you have to understand that heat is a form of energey and cold is a lack of energy... energy will try to get to where there is less energy... the loss is slower due to the insulation, but, the insulation can only do so much... and yes the energy is caused by chemical reactions and the molecules have a harder time finding each other as they get colder because while in any form the molecules bounce around and as they get colder they have less energy to bounce around... so they cannot go as far... this explains why materials shrink in the cold and expand when they get warm, the exception is water, but, that is a different disscusion...

when a substance gets warm enough it will change forms (water turning to water vapor) this helps to explain some of the gasses released by the batteries, some of the heat that causes this effect is created by the batteries being used (chemical reactions cause heat as well as electrical current...

there are some things i have simplified for length, but, i hope this helps someone to understand a little about the reason that cold drains the batteries... a chemist could explain in more detail and answer questions better than me...


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## Uncle Joseph (May 7, 2008)

I too am struggling with this problem in my design. I remember back in the early 90's when I was at college at Michigan Tech. My old chevy caprice would sit for a week or two in the sub-zero temps between drives. I had an Exide Ice Breaker starting battery with 1000CCA and it barely had enough juice left to crank the engine over 3-5 times. Fortunately, that was enough to start the engine. But since we're not using the same battery tech in EVs, I'm not sure what I need to do.

Part of my problem is my work commute. I'll be parking my EV outside for 10-12+ hours after arriving at work, with no supplemental electricity going to the car. My normal commute is only about 12 miles one-way. However, I don't think I'll have enough juice at the end of a 12-hour zero Fahrenheit (or lower) cold-soak to get home.

Resistance heaters can draw huge current loads. I'm wondering if there's a a fairly efficient way to keep the battery pack at a modest 50-60 degrees for the 12-hour down time, while maintaining enough charge to get me home.

It's my understanding that even Li-Ion batteries have cold temperature problems.


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## joseph3354 (Apr 2, 2008)

lifepo batteries do have problems with cold temperature,they don't like to charge in below freezing.you just have to warm them to above freezing temp to charge.they do lose some capacity in the cold as well,but it is minimal.according to manufacturers at -20f they will maintain at least 80 percent capacity.


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## JRP3 (Mar 7, 2008)

I wonder if you start out with a warm pack in the morning how long would it take to drop to ambient temperature? You certainly have a LOT of thermal mass sitting there and an insulated enclosure might just keep it above freezing for many hours.


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## grose (Apr 30, 2008)

I would recommend constructing an insulated box that encloses the batteries. If you don't have access to a plug to run battery blankets your only other option is to use chemical heat. Trusty hand/foot warmers. You'll need at least 2-3 per day. The chemical reaction of those warmers will run the duration of your work time.

I got this idea from the way my saltwater fish are delivered. (Saltwater fish must be kept above 70F constantly.) In the height of winter, they safely make it from Florida to my home in Wisconsin. They are packaged in a Styrofoam container with a chemical hand warmer or two. Works great. I open it up and they are still warm. I bet this method would work just the same for PbA batteries. This is probably something I'll try this winter.


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## tazdotnet (Apr 9, 2008)

when my 1984 caprice was brand new it had an engine block heater that could be plugged into an extention cord to make the car easier to start in the cold, it might be possible to modify one of these to warm the batteries storage area... they already run off of the current from the house so modifiying it to work shouldn't be too hard... there is probably a better solution out there, but, i wouldn't know... i don't know what the heater looked like as it was removed by the previous owner of the car because he could not get the exact model to replace it... but then again he also had the tires replaced and ended up with 3 tires of one size and one of a smaller size and no spare!... on the other hand the car ran pretty good and the interior is clean and all original when i got it for free...


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## Manntis (May 22, 2008)

Lead Acid batteries are highly problematic with Canadian winters. Many LA batteries have liquid electrolyte which freezes when exposed to about -20°C. On my winter beater gas powered car I, like most Saskatchewan residents, have a plug-in battery blanket that warms the starter battery while the car is parked; engine heat keeps it warm while driving. 

However, these battery blankets are too bulky to be used with a volume of LA batteries (technically a battery of cells, but hey) as one sees in an EV.


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## Uncle Joseph (May 7, 2008)

joseph3354 said:


> lifepo batteries do have problems with cold temperature,they don't like to charge in below freezing.you just have to warm them to above freezing temp to charge.they do lose some capacity in the cold as well,but it is minimal.according to manufacturers at -20f they will maintain at least 80 percent capacity.


The batteries warm up as they discharge, don't they? If their capacity loss is minimal in cold weather, then I should be able to drive home (thereby warming the batteries) and plug in the charger, right? I suppose it all amounts to how much the batteries warm up after a 10 mile discharge in sub-zero temperature.


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## Manntis (May 22, 2008)

Uncle Joseph said:


> The batteries warm up as they discharge, don't they? If their capacity loss is minimal in cold weather, then I should be able to drive home (thereby warming the batteries) and plug in the charger, right? I suppose it all amounts to how much the batteries warm up after a 10 mile discharge in sub-zero temperature.


if they're cold enough that it's a problem, they might not give you enough power to drive home in the first place nevermind warm them up on said drive. It's a little like saying "I'm out of gas - I'd better drive to the gas station and get some more"


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## michaeljayclark (Apr 3, 2008)

could you use a separate stand alone battery to power the battery warmers? Since you only need it to warm the batteries at work you could just charge it when you get back home.


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## grose (Apr 30, 2008)

michaeljayclark said:


> could you use a separate stand alone battery to power the battery warmers? Since you only need it to warm the batteries at work you could just charge it when you get back home.


 Theoretically. Battery warmers are AC powered. If you were to use a battery to run this you would need an inverter that has a 110V AC output. The problem I see with this is that resistance heating is pretty energy intensive. You'd kill your aux battery that is powering the heaters long before your shift at work is done. 

On a similar note, I drained the accessory battery in my ICE car once by leaving a 12V electric blanket plugged in. I was surprised how quick it went.


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## michaeljayclark (Apr 3, 2008)

I figured that as well unless you could figure how many batteries it would take to keep warmers on for 8 hours. sure its extra weight but if it kept your batteries warm so they have more of a charge then it would justify it.

Also think about a solar panel to help keep them charged while they are running. I remember being blinded by glare off snow, wonder if this would keep a solar panel running at a good output.


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## Uncle Joseph (May 7, 2008)

michaeljayclark said:


> I figured that as well unless you could figure how many batteries it would take to keep warmers on for 8 hours. sure its extra weight but if it kept your batteries warm so they have more of a charge then it would justify it.


And you would only need it on during the colder months. If _Joseph3354_ is correct about the charge capacity staying at 80%, then I shouldn't have a problem getting home in the cold, even without a pack warmer. I'm wondering if the batteries would warm enough in the 10-mile commute home so that they would accept a charge.


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## Manntis (May 22, 2008)

Uncle Joseph said:


> And you would only need it on during the colder months. If _Joseph3354_ is correct about the charge capacity staying at 80%, then I shouldn't have a problem getting home in the cold, even without a pack warmer. I'm wondering if the batteries would warm enough in the 10-mile commute home so that they would accept a charge.


It's irrelevant what charge capacity stays at if your electrolyte is frozen.

Case in point: I had a car that my neighbour backed into sitting in the repair shop's compound for 2 weeks during a cold snap. Once they fixed the damage I went to pick it up - but the car wouldn't start. The starter battery was frozen. I was able to boost the car, but the alternator was unable to send a charge to the battery itself on the drive home; a battery with slurry or frozen electrolyte will not take a charge, nor give off power.


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## Uncle Joseph (May 7, 2008)

Manntis said:


> It's irrelevant what charge capacity stays at if your electrolyte is frozen.
> 
> Case in point: I had a car that my neighbour backed into sitting in the repair shop's compound for 2 weeks during a cold snap. Once they fixed the damage I went to pick it up - but the car wouldn't start. The starter battery was frozen. I was able to boost the car, but the alternator was unable to send a charge to the battery itself on the drive home; a battery with slurry or frozen electrolyte will not take a charge, nor give off power.


Ok, so maybe I'm misunderstanding. The LiFePo packs won't discharge with 80% capacity at -20f? I guess we're back to warmers then...


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## joseph3354 (Apr 2, 2008)

lifepo batteries do not have an electrolyte that will freeze,their operating temperatures according to the manufacturer are 
-4f to +149f for discharging and 32f to 113f for charging.i incorrectly stated -20f as the lower limit for discharging it is 
-20c.if you charge the batteries directly after discharging(driving) the temperatures of the batteries will be high enough to accept charge.if you have a fully charged pack at -4f you will have 80 percent capacity according to manufacturers specs.


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## Manntis (May 22, 2008)

Uncle Joseph said:


> Ok, so maybe I'm misunderstanding. The LiFePo packs won't discharge with 80% capacity at -20f? I guess we're back to warmers then...


I thought we were talking lead acid batteries, per the thread title


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## joseph3354 (Apr 2, 2008)

yes we were,but somehow got shifted on to lifepo.just wanted to clarify what i had posted.


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## Coley (Jul 26, 2007)

As long as I charge my pack with a timer, so that it is just finishing, when I head for work, low temps weren't a problem this winter. (snow was)

I have a 50 F shop area to pull into, when I get to town, which you won't have.

I investigated all sorts of battery heaters, but didn't need them after all.
I didn't find much, that would work, without plugging it in.


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## Manntis (May 22, 2008)

Coley said:


> As long as I charge my pack with a timer, so that it is just finishing, when I head for work, low temps weren't a problem this winter. (snow was)
> 
> I have a 50 F shop area to pull into, when I get to town, which you won't have.
> 
> ...


charging is a good way to keep batteries warm too - as long as the user is planning it like you, where the battery completes charging just shortly before use.


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