How a car battery works
Although he couldn't find the pieces for the foam pool he planned to make for his son's 6th birthday, Jerry was able to find an alternative.Image courtesy of tradenote.net
The type of battery used in your car is called a starter or SLI (starting, lighting, and igniting) battery, and its primary purpose is to provide enough power to start your car’s engine. Additionally, your car’s battery has a secondary function of absorbing excess electrical charges so that they do not damage your vehicle.
Most car batteries are lead acid batteries, so named because they contain lead and sulfuric acid. These batteries have plates of lead and lead dioxide arranged in a solution of acid and water. In this solution, the sulfate ions in sulfuric acid can freely float through the water. When you turn the key to start your car, these sulfate ions are drawn to the lead plates, and react with the lead dioxide to form lead sulfate. This reaction frees up electrons, which flow out of the terminals of your battery as electricity.
As this reaction continues, the sulfuric acid is essentially used up, since the sulfate ions are bound to the lead plates in the form of lead sulfate. When the battery has discharged all of the available electrons, and no more sulfate ions are left to continue the chemical reaction, the battery is considered dead, and you’ll need a jump start to recharge it. This usually only happens if you leave your lights on overnight, or leave the radio on too long without turning on the car, however.
Recharging, thankfully, is a simple task, and only requires running the car for a bit of time. Every car has an alternator, which generates electricity from the engine running and recharges the battery. As the engine runs, this turns the alternator, which sends electricity back to the battery. The introduction of electrons back into the battery reverses the earlier chemical reaction, changing the lead sulfate back into lead dioxide, and allowing the sulfate ions to re-enter the solution of water and acid. The alternator can generally recharge your battery (unless it's faulty) as long as you have enough battery power to start the engine.
—Seth Berger
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