A battery is a device that creates electrical energy by means of chemical reactions. There are two types of batteries: wet cell and dry cell. A wet cell battery operates by means of a liquid electrolyte solution, while in a dry cell battery, the solution is in the form of a paste. There are a number of different types of wet cell batteries, which may be primary and secondary. A primary battery can be used only until its chemicals are exhausted and cannot react with each other any more, while a secondary battery can be recharged.

Most automotive batteries are wet cell batteries. One common type of car battery, the lead acid battery, is a secondary battery that contains lead, lead oxide, plates, and a liquid electrolyte solution containing 65% water and 35% sulfuric acid. Some of the plates are anodes and attached to the negative terminal, while the others are cathodes and attached to the positive terminal.

When a load is attached to the battery's terminals, a chemical reaction between the lead, lead oxide, and electrolyte solution occurs. As a result of the reaction, electricity flows through the terminals to the load, and sulfuric acid is removed from the solution and is bonded to the plates. When the battery is recharged by passing a reversed current through it, the bonds between the plates and the sulfuric acid are broken and the sulfuric acid returns to the liquid solution, making it available to provide more electricity.

After extended use, a wet cell battery will no longer be able to provide sufficient electricity to the load to which it is attached. This happens because over time, the material in the positive plates flakes off during the normal expansion and contraction of the discharging and charging cycles. As the material flakes off, the plates become smaller and the flakes form a sediment on the bottom of the battery that will eventually make the plates short out and kill the battery completely. A wet cell battery will die more quickly in a hot climate because the heat causes the plates to either accumulate or lose material, and also because water evaporates from the electrolyte solution. In addition, excessive use of the battery, excessive vibration, and overcharging will cause a battery to die faster.

Batteries have been used for over a century, and archaeological evidence shows that galvanic cells may have been used 2,000 years ago. The wet cell battery was one of the first modern battery types to be developed. John Frederic Daniell created the first wet cell battery in 1836. His battery was superior to previous versions because it was safer and more reliable, although it could not be moved and was quite fragile. Since then, a series of many incremental improvements has produced the batteries commonly used today.