Someone told me a long time ago to never put your car battery down on concrete because it will drain the battery. I accepted it without question until recently. Is this true? If so, why does it drain the battery? And would putting the battery on a stack of cinder blocks have the same effect?
Everyone I’ve heard say this have two things in common:
- They are absolutely sure this is correct.
- They have no idea why.
I’ve never heard a convicing argument why this might be true. So I looked it up at Car Talk.
Sure, I’ve heard the old tale, even from a engineer who should have known better. One of the old explanations said it dated from the days when battery cases were made of hard rubber, which would crack if you dropped it on the concrete.
I think it comes from two things: First, a battery that gets taken out and placed on the garage floor is probably on its last legs.
Second, many a battery that gets put on charge is forgotten until it has cooked dry for a couple of days. :smack:
Some 10 years ago I got into an extended wrangle with a friend over this. He was sure that the old tale was true, but couldn’t come up with anything better than “Well, you see, if you put a battery on concrete the charge leaks out!”
So we did a test - two charged batteries side by side, one on a concrete floor, the other on a piece of plywood with small “feet”. I let him chose the time period; the initial experiment covered 5 days. At then end of this, both batteries showed pretty much a full charge, though the one on concrete was 0.1 volts lower. He claimed this proved his theory, but I spiked that by putting it in a car, which started immediately.
The next experiment went nearly three weeks, and there was negligible difference at the end. He wound up conceding that “maybe the effect isn’t all that big” but also asserting that a really long test might prove him right.
If you have every owned a boat, you will see how false this statement is. I remove the batteries from my boat every year and I can tell you that if they were stored on a concrete floor, they would definitely be dead come spring. I’ve done that once. Now they are stored on a wood shelf, and they are always fully charged when I put them back in the boat.
Why would that be? The battery manufacturers mentioned in the Car Talk article linked above say that they often store batteries on the cool concrete floor purposely to preserve the charge. If no one can explain how an insulated car battery can lose it’s charge on concrete but not a wood shelf, I’m going to believe it’s an old wive’s tale (or old grease monkey’s tale).
Placing a battery on a concrete floor will not cause it to self-discharge any faster than placing it on any other surface! In fact, it will probably decrease the tendency for the battery to self-discharge. (See below.*)
The only effect that I can see that causes people like mjhoberiii to insist that it does is that concrete floors (and the ground in general), are generally considerably colder in the early spring than the outside air temperature. By heat conduction, this may cause the battery stored on the ground to be colder than the air temperature.
Battery voltage, like that of all galvanic cells, is temperature-dependent. (Look up the Nernst Equation in a chemistry book for more information.) A cold battery will have less discharge voltage than a warm battery. All you have to do, though, to increase the discharge voltage to normal is to allow your battery to warm up.
*In fact, it would be preferable to store batteries on a concrete floor, as the coolness will slow down the tendency for the battery to self-discharge. Just warm up the battery before trying to use it.
BTW, I know a fair amount about batteries. I was the Electrical Officer on a U.S. submarine, responsible for (among other things) the 126-cell main storage battery with an approximate capacity of 6000 A-hr. I also taught chemistry for five years.
mjhoberiii, the purpose of this message board is to fight ignorance, not perpetuate it. Do you have anything to support your contention beyond your own anecdotal experience?
Wow, thanks guys. Now I can go tell off my friend for being such a jackass. He so wholeheartedly believes this story that he thinks it applies to all batteries, not just the ones in cars. I remember the day we were hanging out at the beach and he kept yelling at me for setting his radio on the seawall. Even if it were true, I thought the plastic would serve as a barrier. But it doesn’t matter anyway. What a dork.
I have the final answer on this.
It was an auto tip in a 1930s Popular Science:
“Leaving a car battery on a concrete floor will ruin it.”
It really happens.
I have seen three concrete floors ruined by leaving car batteries on them
Acid fumes or leaking acid eats away the concrete.
That word “it” has too many antecedents.
I have the real answer.
This started in an auto tip in Popular Science in the 1930s:
“Leaving a car battery on a concrete floor will ruin it.”
This does actually happen.
I have seen three concrete floors ruined by leaving car batteries on them.
Leaking acid vapors eat the concrete.
Nothing happens to the battery.
That word “it” has too many antecedents.
“It” sure does. 
Interesting if that is how it all got started. I haven’t bothered to track it down. I remember nobody being too sure in my dad’s paint and body shop, so we always put the batteries on wood first instead of the concrete itself, just to be on the safe side, but of course just thinking it would ruin the battery.
If that’s how it all got started, they got a hell of lot of mileage out of it.
Hi MidiMagic,
Welcome to the Straight Dope. I saw your post in the old thread about dead car batteries on concrete floors. It’s an interesting response, it would be nice if you could link to some information showing that a 1930s issue of Popular Science contained that line. Even if not it’s still a interesting and clever addition to that thread.
I’ll let one of the mods know about this thread that isn’t really a General Question, or any kind of question.
I was told to put it on wood because concrete would make the battery case crack. Never heard any reasoning to support that.
To the OP;
I like it. Not sure if I believe it, but I like it.
MidiMagic, I did a quick search using some of the info you provided for my search engines, but only could come up with other threads by you such as this one on the Physics forum you also started today. There you mentioned you actually have the 1930’s Popular Science with the original tip in it, but said not to ask you which issue. If we had a specific year and/or month, we could track it fairly quick through on-line archives.
I think this (the graped text) might indicate that batteries that leak acid tend to stop working, rather than anything at all to do with concrete.
It also means that sulphuric acid is not good for concrete floors.
Pronoun trouble?
MidiMagic’s information is accurate, but very much outdated.
There are two things going on here.
The first is that battery cases in the old days were made out of hard rubber. That rubber also happened to be slightly porous. If you left a battery on a concrete floor, some of the electrolyte would ooze out of the battery and onto the concrete. This leaked electrolyte would form a conductive path and slowly drain the battery, in addition to doing whatever damage it would do to the concrete floor.
In 1930, this warning was certainly applicable. In modern times, though, they have been making battery cases out of non-porous plastic for a very long time now, which makes the warning more than a little outdated. Modern batteries are also usually sealed, which means they don’t emit fumes either.
The second thing is that if you have a battery in a warm room with a cold floor, you can set up a temperature differential across the battery. This can cause the electrolyte to stratify, which results in tiny currents flowing through the electrolyte due to the density differences. These tiny currents cause the battery plates to sulfate, ruining the battery. Large battery systems will sometimes have stirring systems built into them to prevent this from happening.
For a battery as small as a car battery though, I’ve read conflicting information about whether you can even get enough of a density variation to get any significant current flow, so it may be that car batteries are just too small to worry about. In order for the electrolyte to stratify, it has to be left sitting still for a fairly long time. This won’t happen overnight. We’re talking about leaving a battery untouched for weeks on end. If you are worried about it, pick up the battery and give it a good shake about once a week.