The lead acid battery in your car does not create electricity like an alkaline battery: It can only store electricity through a chemical reaction.*
Inside the battery are a series of lead and lead oxide plates submersed in an electrolyte containing sulfuric acid and water. When discharging the plates react with the electrolyte creating lead sulfate. Normally this is in a form that's easy to break back down into lead, lead oxide, and sulfuric acid. After several discharges the lead sulfate will crystallize, making it too difficult to break down by a normal electric charge.
Even when the battery terminals aren't connected there is still a chemical reaction taking place between the electrolyte and the plates. Since the battery isn't being charged the lead sulfate is left in suspension longer, increasing crystal growth. There are several trickle chargers on the market that keep current running through unused batteries, slowing this process. If the battery isn’t too badly damaged the crystals can be broken apart with high-voltage “shock” charging.
Once the battery has enough crystals to stop functioning the lead can be remelted and made into a new battery. This lead can be recycled endlessly, so the metal your car battery may have been in several other batteries before you used it.
*How can a new battery have a charge if it can't generate electricity by itself? Fresh electrolyte carries some charge. Car-sized batteries have enough of this electricity to run the starter, but smaller batteries like those used in motorcycles require additional charging before use.
Posted 3503 day ago