The heavy 1859 battery that still starts nearly every car engine
Gaston Planté rolled two lead sheets into a spiral, soaked them in dilute sulfuric acid, and in 1859 created the first battery you could recharge by pushing current backwards through it. It is heavy and stores little energy for its weight, yet it delivers a huge burst of current cheaply, which is exactly what a starter motor wants.
Planté's first cell used rubber strips to keep the two lead sheets apart, immersed in acid of roughly 10 percent strength. Early cells held little charge, so the plates were slowly corroded in a process called forming, which coated them in lead dioxide and roughened the surface. Once generators arrived after 1870, that step got far cheaper. In 1880 Camille Alphonse Faure patented a quicker route: coat a lead grid with a paste of lead oxides, acid and water, then cure it in warm, humid air.
Charged, the negative plate is metallic lead, the positive plate is lead dioxide, and the acid is strong. As the cell discharges, both plates turn to lead sulfate and the liquid becomes mostly water. That has a handy consequence: measuring the electrolyte's specific gravity tells you the state of charge. Crews on diesel-electric submarines wrote the reading on a control-room blackboard as a guide to how long the boat could stay under. It also means a flat battery freezes more readily in the cold, because weaker acid has a higher freezing point.
On paper the reactants could yield about 167 watt-hours per kilogram, but real batteries manage only 30 to 40, since grids, casing and water add dead weight. Each cell is nominally around 2.1 volts. Overcharging splits water into hydrogen and oxygen, which is why flooded batteries let you top them up with pure water, whereas sealed valve-regulated designs, developed in the 1970s, can run in any position.
Cheapness keeps the chemistry alive. In 1999 lead-acid sales made up 40 to 50 percent of the value of batteries sold worldwide outside China and Russia, about US$15 billion. And a 2011 discovery showed their voltage partly depends on effects from relativity.
Source: Lead–acid battery
