Why does your car still start on a battery design from 1859?

Your car still starts on a battery design from 1859 because lead and acid deliver a huge burst of current cheaply, which is exactly what a starter motor needs. The lead–acid battery was invented in 1859 by the French physicist Gaston Planté, and it was the first rechargeable battery ever created. It is heavy and stores little energy for its weight, but it can supply high surge currents, and it is cheap.

Inside, the chemistry is simple. When the battery is charged, it holds its energy in the voltage difference between metallic lead on the negative side and lead dioxide on the positive side, both dipped in sulfuric acid. As it discharges, both plates turn into lead sulfate and the acid becomes mostly water. Each cell has a nominal voltage of 2.1 volts.

Planté's first battery was two lead sheets rolled into a spiral in dilute acid, and its first job was lighting train carriages while they stopped at stations. Most of the world's lead–acid batteries are the starting, lighting and ignition batteries in cars: an estimated 320 million were shipped in 1999 alone.

Their weakness is also a car's weakness. If a lead–acid battery sits discharged for too long, lead sulfate crystallizes on the plates and it loses the ability to accept a charge. Cars spend most of their lives parked, so car batteries suffer the most. That is how a battery left flat for a long time can lose the ability to take a charge.