Battery theory

Battery theory

The primary source for electrical power in all automobiles is the battery. It has undergone many changes through the years. The introduction of hybrid vehicles and the promise of fuel cell vehicles have drastically changed the basic design of an automotive battery. Many different types of batteries are available or under development to exceed the needs of hybrid or fuel cell vehicles. Lead acid batteries have been, and continue to be, the power source for conventional vehicles.

Batteries are devices that convert chemical energy into electrical energy. Chemical reactions that produce electrons are called electrochemical reactions. A battery stores voltage and releases it when it is connected to a circuit. Inside the battery are two electrodes or plates surrounded by an electrolyte. These three elements make up an electrochemical cell. Batteries are normally made up of electrochemical cells connected together.

One of the plates has an abundance of electrons (negative plate) and the other has a lack of electrons (positive plate). The electrons want to move to the positive plate and do so when a circuit connects the two plates. Batteries have two terminals, a positive that is connected to the positive plate and a negative that is connected to the negative plate.

Electrolytes are chemical solutions that react with the metals used to construct the plates. These chemical reactions cause a lack of electrons on the positive electrode and an excess on the negative electrode. When connected into a circuit, the electrons move. The reactions continue to provide electrons for current flow until the circuit is opened or the chemicals inside the battery become weak. At time, the battery has run out of electrons (the battery is worn out). Recharging the battery simply moves the electrons that moved to the positive electrode back to the negative electrode.

The voltage produced by an individual battery cell varies with the chemicals and materials used to construct the cell. Most cells produce between 1.2 and 4 volts. To provide higher voltages, cells are connected together. In addition, there is a limited amount of current available from an individual cell, so to increase available current, cells are connected together. Cells can be connected in series or in parallel, or both.

Battery Hardware:

In order to connect the battery to the vehicle’s electrical system, battery cables are used. They must safely handle the voltage and current demands of the vehicle. Battery holddowns are used to prevent damage to the battery, and heat shields are sometimes used to keep battery temperatures down. Most high – voltage battery packs are enclosed in a box that serves to secure the pack and to keep it within a particular temperature range.

Battery Cables: Battery cables must be able to carry the current required to meet all demands. Normal 12-volt cable size is 4 or 6 gauge. Various forms of clamps and terminals are used to ensure a good electrical connection at each end of the cable. Connections must be clean and tight to prevent arcing and corrosion. The positive cable is normally red and the negative cable is black.

Battery Holddowns: All batteries must be held securely in the vehicle to prevent damage to the battery and to prevent the terminals from shorting to the vehicle. Battery holddowns are made of metal or plastic.

Cooling system: The performance and durability of batteries, especially high – voltage battery packs, are heavily dependent on maintaining desired temperatures. Batteries may be housed in a box or container with a cooling fan. The box not only secures the batteries, but also serves as a conduit for the air from the fan. Some battery designs work best when they are warm. For these designs, the battery box also has a heater. Remember each battery design has its own optimal temperature range.

Heat shields: Some batteries may have a heat shield made of plastic or another material to protect the starting battery from high under hood temperatures. Vehicles equipped for cold climates may have a battery blanket or heater to keep the battery warm during extremely cold weather.


The materials used to make a battery can be used in the future through recycling. Batteries should not be discarded with regular trash because they contain metals and chemicals that are hazardous to the environment. Ninety-eight percent of all lead – acid batteries are recycled. During the recycling process, the lead, plastic, and acids are separated. The electrolyte (sulfuric acid) can be reused or is discarded after it has been neutralized. The plastic casing is cut into small pieces, scrubbed, and melted to make new battery cases and other parts. The lead is also melted and poured into ingots to be used in new batteries.



2 Replies to “Battery theory”

  1. Hatim


    Great article. Thanks for writing it and explaining us the functioning of the battery.

    1. Ibrahim Agourame (Post author)


      Thank you Mr Hatim, Happy that my article helps.

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