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

[Rick]

@Xema

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.

There is quite often a huge temp differential between air temp and the temp of the concrete floor.
The concrete floor is a very big heat sink and can stay very cold even if there is a heater running to warm the air.
Ask anyone that has laid on a garage floor in winter to repair a car. Particularly in snow country.
This brings up what might be the only true part of this tale. The chemical reaction inside the battery slows down as the temp drops. Get the battery cold enough and it may not start the car. So taking a battery out of the car, and leaving it on cold concrete for a couple of days can make it appear to be dead due to the colder temp of the electrolyte, which reduces the voltage output of the battery.

[tracyml2000]

@engineer_comp_geek

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 They’ve been making battery cases out of plastic for a very long time now, so this warning is very much outdated.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.

Thank you for a straight answer. I had already came to that conclusion but needed some “concrete” facts to back it up.

[jasonh300]

@jjimm

“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.

I realize this is a hijack, but maybe GaryT can explain this. I’ve heard from people with old cars who put their original non-radial spare on with 3 modern radial tires and the car was difficult or impossible to control under certain conditions.

[Gary_T]

@jasonh300

I realize this is a hijack, but maybe GaryT can explain this. I’ve heard from people with old cars who put their original non-radial spare on with 3 modern radial tires and the car was difficult or impossible to control under certain conditions.

That’s certainly believable. Radial tires and bias-ply tires have some essential differences in how they react to certain forces. Nevertheless, there is some variation in recommendations about mixing the two types.

Some sources say never mix radials and bias-plies on the same vehicle. Some say avoid mixing, but if you do mix put the radials on the rear. (I have found some accounts of putting the radials on the front with no problem until highway speeds are reached, at which point the rear gets twitchy.) Pretty much everyone says don’t mix types on the same axle.

As to why, read the last item on page 42 here, “Mix effects explained.” The page also has a number of first-hand accounts which are illuminating.