OT: Physics questions: Battery freezing

Hi people,
I have a friend who lives off the grid (solar + wind) and is concerned with the battery charge getting low and the fluid freezing.
My view was that if it is cold enough for the electrolyte to freeze, it will do it fully-charged or flat at about the same temp.
Can someone set me straight with some Physics here please?
Thanks in advance.
Dave
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When battery discharged, lead reacts with sulfuric acid, thus reducing its concentration in water. Lower concentration means a higher freezing point.
i

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I lived in Minnesota for many years before moving to Ca and had many experiences where I ran my battery down to what seemed to be dead without the car starting and worried if my battery would freeze. After studying the subject I found that the freezing point of sulphuric acid solutions follows a snakey curve. Pure sulfuric acid freezes above 40 deg F but once water is added the freezing point drops rapidly. If your battery is fully charged or near that point there is nothing to worry about with the low temperatures we have in this country. The crossover point where the increase of acid concentration causes an increase in freezing temperature occurs at about -90 deg F. (see charts at http://www.unionbattery.com/images/2.6.pdf ). Furthermore , if your battery does freeze and it still contains some acid, it won't freeze hard enough to cause serious damage.
Engineman
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On 1 Dec 2006 17:49:55 -0800, " snipped-for-privacy@aol.com"

Tell a battery that. If a battery is below 1.2SG it will freeze at -20F. At 1.16 it freezes at 0F. at 1.15 it freezes at +5F. 1.2 is 65%, 1.16 is 45%, and 1.15 is about 40% charge (SG corrected for 80F)
Even crystaline ice will damage the separators and cause the spongy lead to flake, ruining the battery.It might not quit right away, but the damage is done.
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Hey Guys,
No one has yet mentioned the hazard a frozen automotive battery presents. It is VERY COMMON for the frozen battery to EXPLODE immediately or with-in a few seconds of the application of "booster cables" or "jumpers" from another battery in an attempt to start the car with a "dead" battery.
If you have lots of good luck, the bottom will just sort of crack and the contents squish/splash; but if you are at the other end of the luck spectrum, you will get doused in acid and/or bits & pieces of fast moving battery container and/or contents.
This can also happen under high heat in certain situations if the battery receives a dead-short across the posts.
Not nice in either event.
Take care.
Brian Lawson, Bothwell, Ontario.
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Thanks Engineman,
snipped-for-privacy@aol.com wrote:

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Dave, I can't do that wrote:

A discharged battery will freeze long before a fully changed battery will freeze. One of the ways to tell if a battery is charged is to use a hydrometer. IIRC a fully charged battery has a specific gravity of about 1.230, which means there is sulphuric acid mixed with the water and making the electrolyte heavier.
Dan
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Dave, popular legend is that a discharged battery freezes more quickly than a charged one. It's too late at night here right now for me to dig up my P. Chem book and justify this belief with fact.
I can share with you my experience that a $$$ deep cycle battey on my boat once froze when it was discharged and burst its container. That was in 0-degree weather. Since that singular experience I have kept my $$$ boat batteries fully charged, and not lost any.
Harry C.
Dave, I can't do that wrote:

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Fact, not legend.
Discharging takes ions from solution and deposits them on the plates. The electrolyte becomes less ionic, more watery if you will. The freezing point rises.
Strictly speaking, it freezes at a higher temperature, not "more quickly".
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snipped-for-privacy@yahoo.com wrote:

OK I just got my Chem Phys hdbk out and here is the "straight scoop". 62nd ed. Pg B154 Sulfuric acid melting point 10.36 deg C BP 338 C (98.3%)
Freezing point depression: Pg D 242 Column % by weight from 0.50 to 100.00 the column for freez point dep stops at 34% and the value is (trumpet sound) 55.28 deg C
SO! At that conc. freezing would be, - 44.92 deg C or - 48.6 deg F
Any more questions? :-) ...lew...
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Thanks Lew,
I love it when I see it in writing. I suspected the freezing would be folklore. I sure hope it does NOT get down to -48 around here. It is +22 at the moment but that's about the High for the day.
Lew Hartswick wrote:

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Dave, I can't do that wrote:

You did note that Lew is talking about a fully charged battery.
Dan
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Dave, I can't do that wrote:

Dave:
I can tell you that the battery in my VW bug froze solid one January night sitting in the parking lot at Pete Field outside Colorado Springs -- the temps were well below zero that night. Went out the next day, tried to start it (nothing, of course), and when I looked at the battery the case was cracked with chunks of ice poking out of it and out of the filler cap holes. Far as I know, it was charged up -- the car had been driven the day before.
Bob
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Something happened to drain the battery. You left the lights on, or something failed and drained the battery. A fully charged battery will not freeze in temps we will see in the states. I have seen -40F temps and my battery made it through just fine. As I kid growing up on the farm we left batteries in farm equipment over winter with no apparent problems. Some equipment was used on a daily basis, some not run until spring. As to the OP, yes a battery that is low on charge can freeze where a charged on will not. Greg
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Greg O wrote:

The thing everybody has missed is that the electrolyte gets depleted over time. The sulphation converts the sulfuric acid to a salt that builds up on the bottom of the battery, and the electrolyte slowly gets turned into water. If you check the Specific Gravity of the electrolyte in a well-used auto battery, you will find it well below what it is supposed to be. This will be true, even if the battery is "fully charged". Of course, the Amp Hour capacity of the battery will be reduced by the same process.
Jon
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I'm curious. Would it be worth it to change out the electrolite after ten years on a forktruck battery? These batteries cost $1600 each and are made light years better than a car battery. The cells are built to be repaired but no one does it anymore - throw away society.
I couldn't justify <afford> a new battery this year and put up with recharging it every single day.
Karl
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It probably wouldn't hurt, altho I've read varying opinions on the success of this, depending on how contaminated the acid/electrolyte is. The key is to charge the everlovin bejeezus out of it before you do so. I read somewhere (mebbe here?) that modern chargers use high-er voltage pulsed DC of various wave forms for more effective charges, etc. Mechanical tapping may dislodge crud/crystallized sulfate, etc. Watch out, tho, in aggressive charging, as these things can be a bomb. I know--a full sized car battery exploded while I was angle grinding something in the same room, and, swear to god, I never found any pieces of the battery!! What a mess.... the acid destroyed the clothes over the next few days. Don't have much experience with grenades, but this hadda be close... You can limit heat damage also by putting the battery itself in a water bath. Bosch published a book on battery charging a number of years ago, about the size of an Airco electrode pocket guide, 6" x 4", about 100 pages. Very interesting. I think that's where I got the pulsing and water bath from. :)
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Karl Townsend wrote:

There's nothing going on that will "wear-out" the acid in normal operation, it's not motor oil. It WILL sulphate up the plates if not maintained correctly, you should check the specific gravity after charging and add acid if it's too low. If it's low, chances are you've got sulphation. If the liquid level is low, add distilled water, normal charging will convert some of the water in the solution to gas. A deep discharge traction battery is a lot different construction than a modern car starting battery, it'll last a lot longer and take more abuse. Heavier per unit of energy stored, too.
There's some cadmium-salt solutions for rejuvenating lead-acid batteries out there, the classic stuff was VX-6, advertised for decades in the back of the mechanics mags. It did reverse sulphating to a certain degree in the old-style lead plate batteries with similar construction to those traction batteries. HF carried some, don't know if they still do. It really can't hurt to pour a slug of it into an old battery to see if you can get more life out of it, it's cheap. Really can't do much harm, either. Might take a bunch with large batteries. Might work long enough to save up your pennies for another one.
Stan
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Serious issue up in Minnesota. My job next week is to remove the batteries from all the tractors, lawn mower, boat etc. and store inside for winter.
A new fully charged battery won't freeze even at -50. Try to start a car in that s#$%, give up, go inside, come back out - now you got a car that still won't start and a froze and busted battery. DAMHIKT
Karl
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Dave, I can't do that wrote:

The greater the charge, the higher the concentration of sulfuric acid and the lower the freezing temperature.
http://www.uuhome.de/william.darden/carfaq4.htm#freeze_points
http://www.nwes.com/using_batteries.htm
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