Is it true that you shouldn't place a car battery on cement?

I have always heard that you can’t put a car battery on the cement because it will drain the battery. Is it true that you should always place it on wood? And why?

I’ve never heard that, and I’ve worked at gas stations for 3 years.

I’ve heard this a lot, and most of the supposed reasons behind it are just silly. Supposedly the concrete somehow pulls the energy out of the battery. It doesn’t.

There are however two elements of truth to this.

The first is that way back in the old days, battery cases used to be made out of hard rubber. The rubber was slightly porous and battery acid could sometimes seep through the cover and form a conductive path with damp concrete. They’ve been making battery cases out of plastic for a very long time now, so this warning is very much outdated.

The second thing is that if you can get a temperature differential across a lead acid battery (like the bottom is on cold concrete and the top is in a warmer room), the electrolyte inside of it will start to stratify. When this happens, you get tiny currents flowing due to the different densities, and these tiny currents cause sulfation of the battery plates and ruin the battery. This is an issue with very large lead acid batteries, and some of these very large lead acid battery systems have ways of stirring up the electrolyte periodically to prevent this from happening (either through stirring rods or they just blow air through it to stir it all up).

While this is very much a known issue with very large lead acid batteries, a car battery is very small by comparison. While this effect certainly occurs to some degree, I’ve read conflicting information about whether it occurs in any significant magnitude in your typical car battery. There’s a good chance that the amount of sulfatiion you get on the plates because of it is pretty much negligible.

ETA: Note that it takes a long time for the electrolyte to stratify. This isn’t something that occurs in a couple of hours. If you are worried about it, go shake your battery up every week or so to stir it up.

What engineer_comp_geek said.

Like the e-mail campaign that lasted for years, for the kid who was “lost” for a few hours, automotive advice can last for decades after technology changes make it obsolete. You can still hear stern warnings to never mix types or brands of motor oil, though the situation that gave rise to the concern is long, long gone. Some people, like tracyml2000, try to verify the information before acting on it or passing it on. Unfortunately, most just pass it on, because they heard it from someone who knows more about cars than they do. They never seem to consider that knowing more than they do doesn’t necessarily mean knowing it all or being right about what they “know.”

Well I pulled a good battery out of my 86 Corolla last October while trouble-shooting a starting problem and it’s been sitting on the concrete driveway ever since. It’s quite dead now so riddle me that! :smiley:

This. Batteries will self discharge. If it sits around on a block of wood, or on concrete, it is going to end up dead if it wasn’t in the first place. Batteries end setting on the garage floor because few shelves are stout enough to hold them. Two years later they are found to be dead and it is the Portland cement that gets the blame instead of the two freaking years it sat without being charged.

Thanks for a good answer.

Note that it isn’t especially common for there to be a big difference between the temperature of a concrete floor and the air just above it. It’s easy to think so, because when you place your hand on the floor it feels cold. But the same is true when you grab a substantial piece of metal that has stabilized at room temperature, the effect being due to the better heat conductivity of the metal.

So, 10W30 can be mixed with 5W30, for example? Because that’s the sort of warning I’ve heard my entire life.

The warning I’ve always heard is that you can’t mix normal oil with synthetic, and you can’t mix different brands (Quaker State and Penzoil, for example). I don’t think either one of these is a problem today.

Mixing 10w30 and 5w30 probably isn’t all that bad either, assuming that your engine is designed for either 10 or 5 weight oil when it is cold, and you aren’t exceeding the temp specs where one should be used over the other. When the engine is cold the oil is going to vary a bit in viscosity because it isn’t going to be perfectly mixed together, but I can’t see that being a big problem. Once the engine warms up you are running 30 weight either way.

Yes it can. It’s hard to know exactly what you end up with – is a 50/50 mix the equivalent of 7.5W30? – but it doesn’t do any harm.

Right, they’re not (and never were, as far as I know). You can buy synthetic/conventional blend put out by the major brands. I’ve heard people speculate that mixing brands is potentially problematic because the different additives may conjoin to make something harmful, but the specs for motor oils require compatibility among brands.

It all goes back to the introduction of high-detergent motor oil. In some cases, when it (the “new, better” oil) was put into engines that had built up years worth of sludge and varnish from non-detergent oil, the detergent oil freed up deposits which migrated to somewhere critical and caused blockage resulting in oil startvation. The proper warning would have been to not put detergent oil into an engine that had been using non-detergent oil, but in typical “better safe than sorry” overreaction, that morphed into “never mix types or brands of oil.” Rather like people forwarding e-mails warning against non-existent dangers because, hey, it COULD be true.

You should store you batteries on a block of wood. It saves energy.

You know how much energy I could save trying to explain to my neighbor that my boat battery is fine on the garage floor if I would just plop it on some wood and call it a day?

I gave up arguing about politics, religion/god, motor oil and whether a battery is okay on the ground.

If necessary, I could be a communist who believes in god, who changes his motor oil with 100% synthetic every 3,000 miles all while my boat battery sits on up to nine blocks of wood over the winter.

If that shuts people up, it saves me a lot of energy!

The way I’ve heard the bullshit artists describe the battery on concrete thing is that the battery and concrete together form a “virtual capacitor” which takes a charge, and then that charge leaks away into the environment. The bullshit artists can sometimes make some rather convincing arguments, I must say, mainly because so few people really understand what a capacitor even is.

I was wondering where that came from. Thanks for posting that.

It’s the thing from Back to the Future. You know, the thing with all of the jiggy-volts.

A related issue is that the battery acid seeping out the battery will eat into the concrete. The battery would be OK, but you’d have white patches (or worse) on the floor. This was even more of an issue when batteries weren’t sealed.

So the warning is more to protect the floor than to protect the battery.

Dude, stay away from the jiggy-volts. That can do serious damage to your junk.

There once was a fellow named Slattery…

Originally Posted by Gary T
It all goes back to the introduction of high-detergent motor oil.

I had always heard that it related to the difference between ash based and paraffin based oils.

“Never mix cross-ply with radial!”

(Cue British PSA with 1970s car out of control, then rolling onto its roof.)

I never, ever understood that ad.