CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Urban legends?

My boss is a bright, thirty-something scientist and owner of a water testing lab who believes the following:

1. 12 volt batteries will discharge if stored on a concrete floor and,

2. Vehicles should not be driven in reverse as opposed to moving forward when first starting out so parks them with the rear end toward the building.

We were told this battery thing in auto shop and there is a technical reason to believe it and a better technical reason to not believe the first technical reason,I will try and find it. I am studying for my Microsoft 70-270 certification exam and will take any excuse to stop.

The only thing I can think of for the reverse idea is to no run somebody over.

I’ll agree with number 1. You shouldn’t store a battery on a concrete floor for any length of time. It will hasten the discharge of the battery. This doesn’t mean it happens overnight, just that the battery will discharge more quickly than it would stored up off the floor.

Number 2 is BOGUS. It doesn’t matter which direction you drive a vehicle after starting it. There is no difference between driving it forward and driving it in reverse.

What does your boss think will be damaged by backing up?

After reading the information on the following web page I’m going to change my mind on number 1:

http://www.thebatteryterminal.com/TechTalk_Batteries_on_Concrete.htm

With regard to #2, about vehicles not be driven in reverse when first starting out, I vaguely recall a problem with the GM Hydramatic transmission in its early years (1940-1948). An old mechanic, who is now deceased, told me about the problem, but I don’t remember the details. There was also a story in “The Model Garage” which was a series that appeared in Popular Science magazine every month from sometime in the 1920’s through 1970. In an issue around 1946, Gus Wilson,the proprietor had a helper, Stan Hicks, who damaged a new car with the Hydramatic that wouldn’t go into reverse. Gus had to round up the parts for the transmission and admonished the owner of the car to put the car in a forward range before backing up as I remember the story. Supposedly these Model Garage stories were based on actual problems. I do remember that the old GM Hydramatic transmissions did not have a “park” position. The owner was advised to leave the car with the selector in the reverse position. As a sidelight, I remember that the 1948 Pontiac had a floor pedal to start the engine. This pedal pushed the starter pinion into the flywheel and also closed the starter switch. On these 1948 Pontiacs equipped with Hydramatic, there was a system of levers that, when one stepped on the starter pedal, it mechanically moved the selector to neutral so that the car wouldn’t start in gear.

You can store a battery on concrete. Todays battery cases are made from plastic. In the old days, the battery cases were made from a rubber compound. And placing those batteries on concrete would kill them for sure.

As to backing or moving foreward when first starting out, I don’t see the logic in that one.

Tester

Yes, those legends belong in the lore of yesteryear; but, not todaysyear.

A number of companies require their employees to park facing out; purely as a safety measure. I have worked as a contractor for 2 such firms, one US and one Asian. In each case I was parking near hydrocarbon processing facilities where fire or poisonous gas could require a quick evacuation.

Storing an old rubber cased battery on concrete would certainly speed up its discharge. I store batteries on a wooden bench in a cool & dry area.

The battery needs a path to ground to discharge. Concrete is a dielectric and the battery case is a dielectric. I don’t see how this is possible.

How many people pull into the driveway, carport or garage front first? I’d say almost everyone, and I haven’t heard any complaints.

I have forgotten the chemistry, though I am sure I could find it on the web, but it turns out that this old wive’s tale is actually true. There is a reason why sitting on a concrete floor is hard on a car battery. I used to understand it completely when I was in college, but now I can just relay what little I remember.

It has to do with the acid concentration stratifying in a battery that is sitting perfectly still. Lead acid batteries like to be shaken or vibrated or temperature cycled once in a while. After being perfectly still for a long while, the acid is slightly stronger in the bottom of the battery. This process is exacerbated if the battery is sitting on a surface that is cooler than the surrounding air (which is usually the case with concrete floors).

If the acid stratifies, there are electrical currents up and down within the cells, and one end of the plates (I have forgotten if it is the tops or the bottoms, tends to sulfate. This reduces battery capacity.

When I was a kid, mechanics used to place batteries on boards rather than directly on the concrete floor. They did not know why, but insulating the battery from the cold floor seemed to help a little to preserve the battery.

With regard to starting the car moving forward, I like the “not running over anyone” theory. Backing up certainly will not damage the transmission.

The link is from Interstate Batterys and explains how the legend got started,look up to Mcparadise

Thank you, oldschool. I believed this, too, until I read the article I posted a link to. We live and learn.

He’s wrong on both counts.
Don’t store a battery on concrete because it will discharge?
And the batteries are stored where prior to the sale? Generally on a metal rack.

Click and Clack’s Q&A column appears in my daily paper every Saturday. It just so happens that they answered this very question in today’s paper.

Their answer: One shouldn’t store a battery on the floor because someone else in the shop may trip over it.

They probably won’t mind if we see the column here.

Posted on Sat, Jun. 27, 2009e

Dear Tom and Ray:

My son, who transports cars for a living, says that we should not put a car battery on the garage floor for more than a few moments while we’re moving it from one place to another. In other words, we should never store it on the garage floor. Why? He claims that it will discharge. He says it happens to them all the time. Now, I’m an electrical engineer. Nothing in my knowledge, training or experience tells me anything about cement garage floors being in any way, shape or form conductive, or in any way a cause of battery discharge. Which one of us is nuts?? Tom

Ray: Your son is. We’ve always been told not to leave car batteries on garage floors, too. But that’s so other mechanics won’t trip over them and crack their heads.

Tom? Cement is not conductive. You’re right about that. But any rechargeable battery ? that’s left anywhere ? eventually will lose its charge. Rechargeable batteries are particularly quick to discharge. Just like your cell phone’s battery runs down when it’s sitting on the kitchen counter overnight.

Ray: There are some people who have told us that this old myth comes from the days when battery casings were made out of wood. If the battery acid spilled out, it could make the wood wet, and create a conductive path to a moist cement floor. I wasn’t around when batteries were made out of wood, so I don’t know. My brother was around, but nowadays, he can’t remember anything before the Teapot Dome Scandal.

Tom: Another theory is that garage floors are simply colder than, say, workbenches. And, as every electrical engineer knows, chemical reactions slow down in lower temperatures. So, while the battery might not be discharging on the cement floor, it might be cooling off, and be less able to pump out its power temporarily.

Ray: That’s why we store all of our unsold batteries on our living-room sofas, Tom. Tell your son that’s what he needs to do, too.

I think each one of us “regulars” needs a “Tom” to their “Ray” then we would have a person to make fun of and say odd things to and not make anybody angry with us.

This would be a way to “vent” the creative smart a** in some of use harmlessly.

I suspect that if we asked the OP’s boss, we would learn that he does not think the battery will discharge if placed on concrete. If he is a scientist, then he likely understands the phenomenon of acid stratification in a lead/acid battery, and what the results are. The issue is not a simple matter of discharging the battery through some sort of external conductivity. It is more complicated than that.

Similarly the ‘expert’ on that web link (who is clearly not a scientist) asks the question of whether a battery is discharged or damamged, but then answers the question by explaining only why it is not discharged. He is not disproving what his dad said. Unfortunately his dad is not around to point out that he is rebutting a statement that was not made.

Batteries awaiting sale are stored on metal racks. The rack is approximately room temperature, and it gets jiggled regularly as batteries are loaded and removed. Also, batteries awaiting sale are (hopefully) not more than a couple of months old when they are sold. The effects of acid stratification are not likely to be apparent in that time even if the new batteries were sitting on a cold concrete floor.

If you are interested in acid stratification, read

http://www.batteryuniversity.com/parttwo-42B.htm

This article does not address the exacerbating effects of sitting on a cold surface, not being agitated, and not getting recharged periodically. One of my texts back in college addressed these factors, but as I said, I don’t recall the details.

Click and Clack have a friend who is a physics professor who they consult occassionally. He sets them straight when they are spectacularly wrong on a question of physics or chemistry. Perhaps they should consult him on this one.

One more thing: I sort of remember was an improvement made in the GM Hydramatic transmission around 1950 to give the transmission “instant reverse”. The GM Hydramatic transmission was installed not only on the Pontiac, Oldsmobile and Cadillac cars, but the Kaiser, Hudson, and Nash automobiles used this transmission. In fact, Ford installed the GM Hydramatic transmissions in its Lincoln. I’m almost certain that there was some reverse problem in these transmissions. Perhaps that is how this legend got started. In 1952, GM modified the transmission to include a city driving range that locked out the fourth gear, but I think the reverse problem had been cleared up a couple of years earlier. Maybe someone who worked on these early GM Hydramatic transmissions can shed some light on the reverse problem.

Actually I found out the hard way that concrete can conduct electricity (~240 VAC). Whether it was the moisture in the concrete or the concrete itself I can’t say. Fortunately for me, it was not a great conductor.

Ed B.

Concrete is a dielectric and the battery case is a dielectric. I don’t see how this is possible.

Concrete is a kind of porous dielectric, and water certainly can get into the interstitial spaces. Freezing and expansion is what causes concrete to spall in climates with cold winters. So I wouldn’t count on it being a perfect insulator.

OTOH, I’m uncertain about battery discharge. I expect that if it were a real problem, there would be big yellow tags on new batteries in the store that instructed the staff “do not store or display on metal racks”. There aren’t.

“I set that battery down just a few days (weeks?, months?, years?) ago. How could it be dead, so soon?!!”