12 volt car/truck battery

[JFletcher]

I bow to your wisdom, it likely is the lead oxide that ruins the battery. I also get my sulphates and sulfides confused.

iirc, sulfides are compounds of sulfur w/o oxygen. e.g., H₂S is hydrogen sulfide. Sulfates are salts that contain oxygen, like MgSO₄. What that has to do with batteries, I have no idea.

220, 221, whatever it takes.

 

[GoldDigger]

What that has to do with batteries, I have no idea.

220, 221, whatever it takes.

A fair amount.
Hydrogen sulfide (rotten egg gas) is found in the material vented from an overcharged battery. (Messed up sulfuric acid). AFAIK no solid sulfides (lead or otherwise) are found inside the battery.
When you start with lead and sulfuric acid (H₂SO₄, hydrogen sulfate) the normal discharge process leads to a coating of lead sulfate on one plate and the conversion of lead oxide to metallic lead on the other. And conversion of the sulfuric acid to water.
The sulfate on the plates as a result of normal discharge current flow is soft and spongy and can be converted back to metallic lead by normal charging voltages.
When we say a battery is sulfated we mean that the "good" sulfate has spontaneously converted over time to "bad" sulfate without changing its chemical composition.
A secondary effect of sulfation is that when the battery is recharged as much as it can be, the specific gravity of the electrolyte will be lower than it should be because of the missing sulfate in the dilute sulfuric acid electrolyte mix.

 

[Electric-Light]

Concrete is alkaline and is easily eaten by acid. Ever seen smooth plain concrete near pickle shelves? You can see the concrete etched from spilled pickle juice. Did concrete get etched under the batteries in the olden days? That would support the porous leak theory.

This page explains acid tends to gather up near the bottom and lean out the top and encourage sulfation towards the top.

http://batteryuniversity.com/learn/article/water_loss_acid_stratification_and_surface_charge

 

[GoldDigger]

This page explains acid tends to gather up near the bottom and lean out the top and encourage sulfation towards the top.

http://batteryuniversity.com/learn/article/water_loss_acid_stratification_and_surface_charge

Useful information, but not particularly relevant to the discharge on concrete phenomenon.
One helpful thing about stratification is that charging the battery fully also cause bubbling that mixes the electrolyte.


mobile

 

[Electric-Light]

Useful information, but not particularly relevant to the discharge on concrete phenomenon.
One helpful thing about stratification is that charging the battery fully also cause bubbling that mixes the electrolyte.


mobile

Concrete almost always stay colder than the ambient air temperature in moderate climate. Supposed theory I read is that it cools the bottom like a cold plate thus contribute to what that site is saying.

 

[GoldDigger]

Concrete almost always stay colder than the ambient air temperature in moderate climate. Supposed theory I read is that it cools the bottom like a cold plate thus contribute to what that site is saying.

A valid point, but only if the battery is being used while sitting on concrete. The stratification only develops in the first place during charging or discharging, and will not go away on its own even if the temperature is uniform from top to bottom.

 

[Electric-Light]

A valid point, but only if the battery is being used while sitting on concrete. The stratification only develops in the first place during charging or discharging, and will not go away on its own even if the temperature is uniform from top to bottom.

If the battery is kept on a mild hot plate, the bottom is hotter and would stir the electrolyte through convection, so I would say it would go away in the right conditions

 

[tom baker]

Exact same question came up on Car Talk last weekend, its an myth.

 

[Frank DuVal]

To bring you up to speed, Car Talk has been in reruns since 2012!

Tom Magliozzi passed away in November 2014.