Subsection 4.4.2 Batteries
Batteries are electro-chemical, direct-current power supplies. Batteries store and deliver electrical energy through a chemical reaction. Batteries consist of several electro-chemical cells, each containing an anode, cathode, and electrolyte.
When connected to a circuit, the anode releases electrons into the external circuit, while the cathode absorbs them, generating an electrical current. Each cell creates around 1.5 volts depending on the battery chemistry.
The chemical energy stored in a battery is finite, and is measured as its ampere-hour capacity. As current is drawn from the battery the chemical energy is depleted, at which time the battery must be replaced or when possible, recharged.
Wet cell batteries contain a liquid electrolyte that is typically a mixture of water and sulfuric acid. Lead-acid batteries are the most common type of wet cell. Wet-cell batteries are used where large power capacity is required, such as for uninterruptible power supplies and for starting small engines.
Dry cell batteries contain an electrolyte in a solid, semi-solid, or gel-like state. Alkaline, nickel-cadmium (Nicad), lithium-ion, and nickel-metal hydride batteries are all dry cells. Dry cells are commonly used for low-power purposes, such as flashlights and portable equipment.
The state of charge of a battery usually cannot be determined easily or accurately. For lead-acid batteries the approximate charge is determined by measuring the density of the electrolyte with a hydrometer, while the approximate charge of the Nicad batteries is determined by measuring the cell voltage.
