Okay, this is one for all you chemistry experts out there...

What exactly happens when a car battery goes dead?

Why does it lose it's charge? Why can it be recharged? And why can't some not be recharged?

is your friend. (for basic fact finding on non political topics)

http://en.wikipedia.org/wiki/Lead_acid_battery

http://en.wikipedia.org/wiki/Sulfation

Plus there's the stress degradation. Basically it's almost always the electrodes unless the battery exploded.

A famous quote you'll find in many forms: "most batteries don't die natural deaths, they are murdered by their owners."

batteries work by creating a vast difference in electric potential. One area is highly negative (-) and is swarming with extra electrons. The other part of the battery is just the opposite - highly positive (+). Just like in a dam: you create a big difference, this time with water and elevation, not electrons and charge. A battery produces electricity by letting the electrons "flow" from the negative area to the positive. Once the battery has come to equilibrium, there is no more flow so no more electricity. Does that make sense?

The typical battery has two compartments. One has reduced metal ions in solution which carry extra electrons above the valence shell, and the other has an unreduced metal with a greater affinity for electrons than the first. When a circuit connects the two compartments, electrons flow from the reduced ions to the unreduced metal, while a salt bridge between the two compartments prevents the build up of a repulsive electric charge by releasing oppositely charged ions into each compartment.

When the battery is "dead" it has reached chemical equilibrium, and the metal with the greater affinity for electrons is now the only one which exists in reduced ionic form. This process can be reversed simply by applying an electric current stronger than that produced by the battery in the opposite direction, forcing the metal with the greater affinity for electrons to lose it's extra electrons and returning the other metal to ionic form. I'm not sure why some batteries cannot be recharged, but I would guess that it's due to corrosion or other damage to the apparatus.

edit:spelling

I found your question interesting and did a quick search, this site explained a number of things I dd not know.

http://science.howstuffworks.com/question390.htm

I also know from personal experience that if your having trouble starting your car.
Most newer cars have an electronic fuel pump and it needs a certain voltage to operate If I remember its somewhere around 11 or 12 volts. when your battery gets weak it does not have the current to activate the fuel pump, the engine will crank and crank but with out fuel it will not start. So invest in an inexpensive multimeter (cost about $10 at sears) and check the battery output it should be above 13.something, then check the alternator to see if it is putting out the same. So if the alternator is not producing theres the culprit, if it is working the battery may be on its last legs.