Battery on the ground

I'm sixty, and learn stuff every day. I love it. All my life, I've believed this. Always sat my batteries on a piece of 2 x 6 on concrete. Good, one less thing to do.

Steve

were bad already. ?That's

tests a couple of them

Yeah, I noticed that too. So much for the credibilty of that explanation!

BTW, Bob, Don didn't say that -- the website said that.

Fact remains, I have a couple of batteries sitting on a concrete garage floor in MN that self-discharge no more rapidly than those in my fiberglass boat. Years ago I set one battery on a bit of 3/4" plywood and another on the concrete floor right next to it. No difference in self-discharge after several months. I quit worrying about it at that point.

YMMV.

I read this again more carefully. I see what you're saying. If a heatsink like a concrete floor cools the battery below the dewpoint of ambient air, condensation will occur on the battery and provide a discharge path. In such a case, the concrete floor would also be damp for the same reason that the battery is. That has nothing to do with self-discharge, merely indicates the condition that could result in self discharge. That doesn't happen in my garage, but I can certainly imagine that it does in some climates.

I think you broke the code.

>

On Thu, 20 Mar 2008 13:48:28 -0400 in rec.crafts.metalworking, clare at snyder dot ontario dot canada wrote,

Right. I was wondering if anybody who knew was going to post. Conditions have to be right for it to occur, which is probably why so many don't understand it.

So, since the battery in my '04 Lincoln is next to the spare under the trunk mat and the one in SWIMBO's '03 Buick is under the back seat, that should be a bennie for us, since the batteries won't be jubjected to all that engine heat when the cars are running.

Jeff (Who's old enuf to remember when many car's batteries were located under the right front seat.)

attery on the ground or concrete that it

always seen this story; the only thing I could think of is that damp concrete definitely exudes some sort of alkali vapor; leave a piece of aluminum in a damp garage all winter and see all the crud it accumulates. maybe that neutralizes the acid in the battery, although if it's in the air i don't see what good a piece of plywood would do unless it was wide enough that the battery was in its own microclimate.

It's more than a theory. Submarine batteries typically had "bubblers" installed in each cell to keep the electrolyte stirred. This prevented temp stratification in the large cells. See

Randal

Don Foreman fired this volley in news: snipped-for-privacy@4ax.com:

Thank you Don. I was having near-irresistable urges to post something similar. Apparently, in acid, Brownian motion ceases. Heavy molecules settle out.

LLoyd

If I pour some battery acid into a beaker, set the beaker on a cold plate and ensure that it is not physically disturbed, do you assert that the solution will stratify after some period of time such that samples drawn from near the bottom will have higher specific gravity than samples drawn from near the top?

Thank you Randall - that is one of the cites.

Most definitely.

[ ... ]

Well ... I remember that my MGA's batteries (two 6V ones in series to make 12V) were one behind the driver's seat and one behind the passenger's seat -- with a jumper cable looping over the driveshaft.

One was over the exhaust pipe, and the other just over open air, and I don't remember one failing any faster than the other.

Enjoy, DoN.

OK, perhaps I should have said lower pH or higher concentration. Even plain water with a temperature gradient will have higher s.g. where colder, down to 39F anyway.

Absolutely, unequivocally NOT.

Even if the ground is frozen YET the battery is fully charged, it still will not discharge.

I can't believe that this wife's tale still persists and that some will go to their grave arguing that it is true.

j/b

Pardon my lack of tact but, BULL.

I'm in the same age bracket as Steve and believe in the acid separating from the water in strata due to chilling it. Ionic flow must take place for battery operation to take place. Without the acid mixed in evenly, only small areas of the plates can conduct electrons. If only 5% is available, the effective resistance is excessive and makes it look dead.

Martin

Mart>>> I have heard that if you sit a battery on the ground or concrete that it

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On Fri, 21 Mar 2008 14:55:13 -0600 in rec.crafts.metalworking, Don Foreman wrote,

Why wouldn't the cold acid be a more dense than the warm acid? But actually, the acid will stratify due to gravity without even a temperature gradient if it sits long enough without stirring.

Good proposal for an experiment, by the way, but you would have to use a battery not a beaker.

Let's see if I can keep the polarities straight. If you put a lead-acid battery on your cold plate and establish a temperature gradient through it, the warmer top will try to generate a higher voltage than the colder bottom and you will have a current flowing within the cell that discharges the battery. The top side reaction depletes the H2SO4, making the density gradient worse.

When the temperature equalizes, the current flows the other way and the plates even out enough for the same thing to happen again the next day. Without the internal circulating current, nothing much happens.

OK, that is probably pretty badly bollixed up, but you get the idea. It has nothing to do with porous cases or external leakage. No doubt somebody on sci.electrochem.battery can explain it better.

There is no completion of the circuit. So, one has acid-soaked wood and acid-soaked concrete. It is doubtful that this acid-soaked environment would exhibit enough conductance through the reverse path, to discharge a lead-acid battery.

j/b

I like this explanation. Can anyone describe the path the electrons would take to discharge a battery through an acid soaked floor?

Engineman

This is the only theory that makes any sense to me.

Restating what I think you have tried to assert, with slight modification and a bit of embellishment if I may:

If there is a vertical temperature gradient then cell voltage at the top must be different from cell voltage at the bottom because cell voltage depends upon temperature as well as electrolyte specific gravity (s.g.).

If the cell's EMF is different at top than at bottom then current must circulate within the cell. Example: I may have the signs wrong, but let's say that the cell EMF is 12.20 at the bottom and

12.25 at the top. There's a net loop (vector sum) EMF of 0.05 volts so enough current must circulate to produce .05 volts of IR drop in the plates. (Kirchoff's law) But note that the circulating current at the top is opposite in direction to the current at the bottom, so it has the effect of charging in one region while discharging in the other region. This eventually will result in changing the specific gravities of the electrolytes in these respective regions until the difference in s.g. offsets the difference in temperature so difference in EMF becomes zero and a state of equilibrium is reached. Stratification has thus necessarily occurred due to electrochemical action and in spite of kinetic diffusion. I'm quite sure that kinetic diffusion would prevent battery acid from stratifying in a beaker, but (as you noted) a beaker is not a battery.

The net charge of the cell would not have changed except that the charge-discharge process is not 100% reversable and efficient (not to mention IR losses) so there must be some net loss of charge until equilbrium is reached.

If the battery is temperature cycled from day to day, then this process could happen periodically. In that case, some charge would be lost with each cycle.

I don't know anything about how or if stratification would cause plates to "sulfate" or whatever. That probably depends as much or more on battery construction, age and history as anything else.