Auto Part Insights - How Does a Car Battery Work

How does a Car Battery work?

A standard 12-volt car battery generates electrical energy or current with the help of electrochemical reactions that take place inside it. It is this current that starts your car engine when you turn the ignition key. A car battery also acts as reservoir storing electrical energy derived from the alternator of the car. In case you are wondering what an alternator is, might help to consider it as a generator that works on the principle of electromagnetism to produce current that charges your car battery while the engine is running. The stored electrical energy in the battery powers all electronics on-board your car including lights, stereo, air conditioning etc. Hence, the cycle goes like this: a charged battery is used to start the engine and a running engine is used to run the alternator that charges the battery again. Back to our topic, a reversible chemical reaction between three main constituents of the battery i.e. Lead (Pb), Lead Oxide (PbO2) and Sulfuric Acid (H2SO4), allows the car battery to not only produce electricity but also store it in the form of charged cells inside the battery. A cell constitutes an enclosure in the battery that contains two types of metallic plates and two terminals (i.e. positive and negative). One plate is covered in Lead and the other in Lead Oxide. All cells in the battery (six cells in a 12-volt battery) soak in a common chemical bath of 65% water and 35% Sulfuric Acid called Electrolyte. The chemical reactions between the two metallic plates in the acidic medium produce electrons that form the electrical charge. The charged particles travel from the positive terminal of the cell to the negative terminal. The same reaction takes place in each cell and the common Electrolyte in the battery transports the electrical charge from one cell to another finally resulting in transfer of charge from the positive terminal of the first cell to the negative terminal of the last cell. Each cell produces 2-volts of electricity and together 6 cells combine to produce 12-volts. It is worth mentioning that the positive terminal of the first cell is the positive terminal of the battery and the negative terminal of the last cell is the negative terminal of the battery. The flow of electrical charge from the positive terminal of the battery to the negative terminal powers any circuit connected between the two ends. All electrical systems of the car are directly connected to a circuit between the two terminals of the battery and receive electrical energy through this process. The usage of electrical charge drains the battery or discharges it. But that's when the alternator takes over. A running car engine powers the alternator that produces electrical charge (electrons) and sends it through the negative terminal of the battery towards the positive terminal. This way, the electrons travel back in the system reversing the chemical reactions in the battery and restoring the chemicals to their normal state. Hence the battery is replenished and ready to produce 12-volts of charge again. James Rodham



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