Car batteries are typically made of six galvanic cells in a series circuit, with each cell providing 2.1 volts for a total of 12.6 volts at full charge. An automobile battery is an example of a wet cell battery, with each cell consisting of alternate plates made of a lead alloy grid filled with sponge lead plates (cathode) or coated with lead dioxide (anode). Each cell is filled with a sulfuric acid solution, which is the electrolyte. The majority of cars use lead-acid batteries, which are made up of alternating plates of lead and lead oxide submerged in a bath of sulfuric acid electrolyte. Hybrid car batteries are typically nickel-metal hydride or lithium-ion, while electric car batteries are almost universally lithium-ion. Lithium-ion cells are the most popular because of their cost efficiency, offering the most optimal trade-off between energy storage capacity and price. The exact chemical makeup of each electric cars battery is a closely guarded secret, but the major components include steel, aluminum, lithium, manganese, cobalt, nickel, and graphite.