Battery on Concrete...UL?

Factual Questions
1

OK, many of you know I’m an ME, not an EE or physics major, so don’t make fun of poor old Una for asking this question.

This was brought up by a friend who is actually pretty smart but somewhat argumentative (he’ll even argue with ME over coal power plant facts, I mean, that’s like competing with Venus Williams at tennis.)

He claims that you should never set an automobile battery on a concrete surface for storage, because it will create a “virtual capacitor” and drain itself much more quickly than if you set it on a wood or steel surface. I have tried to argue that I don’t see how on earth this could happen, but I confess I’m not an expert on electrodynamics or electrostatics so I feel like I don’t have a good position to argue from.

I have also heard several auto mechanics repeating this as being true, but have never seen any kind of warning or mention by a battery manufacturer. I did talk to one guy who worked at Delco battery for 30 years who also asserted it was true, but it was a “secret”, and that’s why no one talks about it.

OK, all you auto buffs, physics majors, double-E’s, and mulatto touch-typists out there - is there any truth at all to his assertion, and if so please explain it to me!

2

I don’t know about the truth of the statement, but as an electrician, I do know what surfaces will conduct electricity and what won’t - you gotta know what you’re standing on after all if you’re gonna play with voltage. Concrete will conduct electricity, and relatively well at that. I think it has something to do with the water used to mix it (I’m not sure though, feel free to call me on that). So it does seem logical for me that a battery will drain when set on a conductive surface.

I don’t, however, see how steel will be much better than concrete, unless there’s some other reason besides concrete’s conductive capabilities that drain the battery.

3

I’m not saying that it’s not true, but I had an old interstate battery I pulled out of a car, it sat on the garage floor(concrete) for a year and a half through winter, cold winter, threw it in an old station wagon, V8, hasn’t started in years and it turned it over wonderfully. The car didn’t start but it turned it over longer than I expected it to. I believe the engine turning over lasted about as long as a normally charged battery would have lasted. - True story.

4

As a physics geek, I do not know how this (virtual capacitor on concrete) could be true. If the terminals in the battery are on the top, and not connected to anything, and the battery is sitting on a surface with no weird things like a stream of electrolyte running down from the terminal to the surface to conduct stuff, I have no idea how it could matter what surface it sits on.

I’ve been wrong before, though.

Of course, there are ways for it to drain if you have some way for the electricity to be conducted down to the surface…

5

I hadn’t thought about the terminals, doug, good point. It also didn’t click for me why concrete would drain it and not steel.

6

My OP may not be entirely clear - I mean that the plastic case of the battery is set on the concrete, with the terminals up in the air and not connected to anything at all. Like douglips said, I can’t see how it could possibly be, but a few people I know seem to think it’s true.

Anyone else have some ideas?

7

This is not true! I worked in a battery supply house for about 7 years. We stored many of the batteries of concrete. Sometimes a customer would see the batteries on the concrete floor and request another battery from the wooden shelves because concrete kills batteries. Most of these customers were old men. Once I asked one of the older employees about this and he said about 30-40 it was true, but it hasn’t been true for a long time.

8

Click and Clack have an answer here, the gist of which is it used to be true, but isn’t anymore.

9

that should be 30-40 years ago.

If you want to talk to an expert call your local battery distributor. It should be listed in the yellow pages.

10

OK here is a topic I know a little about having spent about 33 years in the automotive business.
Back when I first started in the car business batteries had hard rubber cases and the tops of the batteries were covered in tar (yes soft gooey tar) as the battery got older the tops got softer and dirty. This dirt was a combo of junk in the air (dust) and electrolyte that had spattered out of the battery vents (on the caps) this mixture was conductive and that combined with the hard rubber cases (mentioned by Click and Clack) would lead to self discharge.
One other item not mentioned elsewhere is that concrete is generaly cooler than the surrounding air. As you no doubt learned in Chem 101 reactions slow down when heat is removed. A new fully charged battery will only put out about 50% of it’s rated capicity when chilled to 30 degrees F. So a couple of days on cold winter (concrete) floor and the car will be hard to start.
The modern plastic cases don’t have the problems of the older rubber ones, but I still clean the top of the case when I service a battery and I don’t place batteries on the floor due to the temp issue.
Rick

11

here’s to relating 2 seemingly unrelated things. This thread and what I heard about radiation given off by concrete. I remember hearing about concrete sidewalks in mid west area being so high in radioactive stuff that a pregnant woman should not sit on in so as not to harm her child. - butwhat would radiation due to a battery - i’m not sure

12

I think even Cecil addressed this in passing during in one of his books. A clean battery will not discharge any faster on a concrete floor. But, as Rick mentioned, a concrete floor is often colder than other flooring, and leaving a battery there will make it colder, and thus reduce its capacity and max starting current, until the battery is warmed back up again. Actually, any battery will discharge slower when cold, so it should last longer on the concrete floor if it is colder (that’s why you’re supposed to keep batteries in the fridge). The only thing is you need to let the get back to room temperature before using them :slight_smile:

Arjuna34

13

Don’t put your batteries in a freezer though- you might freeze them! That’s definately not good for long life.

Arjuna34

14

Ironically, k2dave, the person best qualified to answer your question is probably Anthracite… But I’m here first, so I’ll field it. The reason that concrete is so radioactive, is that it’s often made from coal cinders, among other things. Everything that you pull out of the ground, including coal, has trace amounts of radiactive material in it. Usually, this is primarily in the form of very heavy metals, such as uranium and thorium. Well, when you burn something, it tends to be the heavier components that get left behind as cinders, so cinder has a higher concentration of the radioactive materials. I’m not sure how hazardous it is, but you can definitely get some clicks on a Geiger counter from cinder blocks.
Batteries, on the other hand, are filled with (usually) sulfuric acid, and cased in high-quality metals. The acid is too light to have significant amounts of radioactives in it, and the casing, if anything, would have lower than natural radioactivity levels, since it’s purified material, not just made from leftover scraps like concrete. The only significant contributor to radioactivity would be the lead electrode, but even at that, it’d be no worse than any other chunk of lead of the same size and purity.

15

I read recently that this used to be true. As Rick said, batteries used to made of hard rubber, before the use of plastics. The article I read stated that the discharge was due to the porousity of the rubber, it is actually more porous than plastic and had a leaching effect. Perhaps this was a chemical reaction (batteries are acid, concrete is not). Anyway , now that batteries are cased in plastic, this is no longer a problem

16

thanks Chronos
but I ment the actual radiation given off by the concreate effecting the battery. i.e.
I assume alpha particals just bounce off the case presenting no problem. Beta Part. probally get into the lead plates and add electrons to both + and - plates. gamma rays, not sure what they will do could act like a metal in the microwave.
now does concreate have this much radioactivity to cause any damage to a battery - I don’t know

17

Oh, sorry… I saw, “radiation due to battery”, should’ve realized you meant “do”. It probably wouldn’t do anything; a car battery is a lot simpler than a living organism, and so a lot tougher to mess up. Radiation might cause a capacitor to discharge, and it might, in principle, ionize a few more atoms in the acid, making it slightly more conductive, but that shouldn’t be a big effect.

18

See this Car Talk column for the definitive answer from Tom and Ray, which exactly agrees with what Rick said.

19

DAMN! A coal-related question, and I’m not the first!

Anyways, FYI, here are some representative values I’ve personally seen for some radionucleides found in coal ash:

Thorium - As high as 5 ppm.
Uranium - Wyoming coal, as much as 7.6 ppm. Eastern coal, typ. 1.6 ppm.

Say you take a typical midewestern coal plant burning 200 tons of 5% ash Wyoming coal per hour. 7.6 ppm of Uranium in the ash equates to 200 ton * 2000 lbm/ton * 0.05 lbm ash/lbm coal * 0.0000076 parts Uranium/parts ash = 0.152 lbm Uranium released per hour. This nearly all goes into the bottom and fly ash of the boiler, at a typical 20%/80% split (typically, only flyash is even considered for block/brick/concrete use). So in the fly ash hoopers, you get about 0.80.152 = 0.122 lbm Uranium per hour. A flyash silo (where the hoppers empty to) typically has an 80-hour full-load capacity, so if full has about 800.122 = 9.73 lbm of Uranium in it. Not that much, but certainly enough to wonder about…

This has no bearing on my OP. I just like coal. :slight_smile:

20

In response to the original question:

All else being equal, a battery will not discharge any faster if set directly on a concrete floor. It could set directly on a metal surface, for that matter, and it shouldn’t make any difference.

The discharge rate of a battery is primarily a function of what’s placed across its terminals, not what it’s setting on.

Now I said it “shouldn’t” make a difference. Under certain conditions, setting a battery directly on a concrete floor could make it discharge faster if there is a temperature gradient within the floor itself.

How? The following is a poorly-drawn picture of a typical car battery:

          A
  ----------------
  |   +      -   |
D |   O      0   | B
  |              |
  ----------------
          C

Six cells are in series from D to B. A temperature gradient between D and B shouldn’t cause any problems, but a temperature gradient between A to C could cause currents to flow inside the battery from A to C, or C to A, depending on the direction of the temperature gradient. Why?

The open-circuit voltage for any battery, even if “fully charged,” is a function of temperature. Thus when the battery is in thermal equilibrium, the voltage at the A-side will be identical to the voltage at the B-side (for each cell or group of cells). But if there is a temperature gradient from A to C, the voltage at the A-side will be different than the voltage at the C-side. This difference in voltage across the low-impedance path of any particular cell will cause a current to flow. This current produces heat, and thus consumes energy from the battery.

Moral of the story? If placing a thermal insulator between the battery and the floor (such as a piece of wood) minimizes temperature gradients within the battery, the battery may keep its charge for a longer period of time.

Michael Craft
Electrical Engineer
University of Dayton
Dayton, OH
mcraft@udri.udayton.edu