car battery is a rechargeable battery that is used to start a motor vehicle. Its main purpose is to provide an electric current to the electric-powered starting motor, which in turn starts the chemically-powered internal combustion engine that actually propels the vehicle. Once the engine is running, power for the car’s electrical systems is still supplied by the battery, with the alternator charging the battery as demands increase or decrease.

Typically, starting uses less than three percent of the battery capacity. For this reason, automotive batteries are designed to deliver maximum current for a short period of time. They are sometimes referred to as “SLI batteries” for this reason, for starting, lighting and ignition. SLI batteries are not designed for deep discharging, and a full discharge can reduce the battery’s lifespan.

As well as starting the engine, an SLI battery supplies the extra power necessary when the vehicle’s electrical requirements exceed the supply from the charging system. It is also a stabilizer, evening out potentially damaging voltage spikes.While the engine is running, most of the power is provided by the alternator, which includes a voltage regulator to keep the output between 13.5 and 14.5 V. Modern SLI batteries are lead-acid type, using six series-connected cells to provide a nominal 12 volt system (in most passenger vehicles and light trucks), or twelve cells for a 24 volt system in heavy trucks or earth-moving equipment, for example.

Gas explosions can occur at the negative electrode where hydrogen gas can build up due to blocked battery vents or a poorly ventilated setting, combined with an ignition source. Explosions during engine start up are typically associated with corroded or dirty battery posts. A 1993 study by the US National Highway Traffic Safety Administration said that 31% of vehicle battery explosion injuries occurred while charging the battery.The next most common scenarios were while working on cable connections, while jump starting, typically by failing to connect to the dead battery before the charging source and failing to connect to the vehicle chassis rather than directly to the grounded battery post, and while checking fluid levels. Close to two thirds of those injured suffered chemical burns, and nearly three fourths suffered eye injuries, among other possible injuries.

Electric and Hybrid cars

Electric vehicles (EVs) are powered by a high-voltage electric vehicle battery, but they usually have an automotive battery as well, so that they can use standard automotive accessories which are designed to run on 12 V. They are often referred to as auxiliary batteries.

Unlike conventional, internal combustion engined vehicles, EVs don’t charge the auxiliary battery with an alternator—instead, they use a DC-to-DC converter to step down the high Voltage to the required float-charge voltage (typically around 14 V).^[7]

Battery History

Early cars did not have batteries, as their electrical systems were limited. A bell was used instead of an electric horn, headlights were gas-powered, and the engine was started with a crank. Car batteries became widely used around 1920 as cars became equipped with electric starter motors. The sealed battery, which did not require refilling, was invented in 1971.

The first starting and charging systems were designed to be 6-volt and positive-ground systems, with the vehicle’s chassis directly connected to the positive battery terminal.Today, almost all road vehicles have a negative ground system. The negative battery terminal is connected to the car’s chassis.

The Hudson Motor Car Company was the first to use a standardized battery in 1918 when they started using Battery Council International batteries. BCI is the organization that sets the dimensional standards for batteries.

Cars used 6 V electrical systems and batteries until the mid-1950s. The changeover from 6 to 12 V happened when bigger engines with higher compression ratios required more electrical power to start.Smaller cars, which required less power to start stayed with 6 V longer, for example the Volkswagen Beetle in the mid-1960s and the Citroën 2CV in 1970.

In the 1990s a 42V electrical system standard was proposed. It was intended to allow more powerful electrically driven accessories, and lighter automobile wiring harnesses. The availability of higher-efficiency motors, new wiring techniques, and digital controls, and a focus on hybrid vehicle systems that use high-voltage starter/generators have largely eliminated the push for switching the main automotive voltages.