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MORE ABOUT BATTERIES

Charged Up

Batteries run everything from cameras to cars and are a source of long-lasting dependable energy, but knowledge of their use and behaviour is critical


A battery is a collection of several galvanic cells, all connected in series to produce a greater voltage than a single cell could. A wet cell battery contains anodes and cathodes, and a liquid electrolyte solution that is 65% water and 35% sulphuric acid. Anodes are attached to the negative terminal, while the cathodes are 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 which electricity begins to flow through the terminals to the load, and sulphuric 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 sulphuric acid are broken, and the sulphuric acid returns to the liquid solution, making it available to provide more electricity.
Batteries are either single-use or rechargeable. Single-use or primary battery can be used only until its chemicals are exhausted and cannot react with each other anymore. They have one life cycle and must be replaced when drained. Examples include alkaline, carbon-zinc, lithium, silver-zinc and zinc air.
Rechargeable batteries, also known as secondary cells or wet cells, can be recharged and used repeatedly. There are four basic type of wet cells: lead-acid, nickel-cadmium, silver-zinc, and silver-cadmium.
Factors to consider when choosing a battery are its cost/benefit ratio, lifespan, performance, run time, vibration resistance, and its maintenance needs. Wet cell batteries are used in cars, trucks, tractors and other motor vehicles to provide the spark to start the vehicle. A standard 12-V car battery consists of 6 lead acid cells each of which produce 2 volts. A disadvantage is that they are extremely heavy, but on the plus side, the redox (reduction-oxidation) reaction that occurs is readily reversible, allowing them to have a long, reliable and useful life.

Lead Acid Batteries
These are medium to large flooded cell batteries, maintenance-free, vented and rechargeable. They contain an anode of lead peroxide, a cathode of sponge lead, and an electrolyte solution, are non-spillable and contain some acid electrolyte. They are the most widely used secondary cells, commonly in automobiles, motorcycles, boats, outdoor power equipment, emergency lighting and UPS. Two other types of lead acid batteries are absorbent glass mat and gel cells.

Absorbent Glass Mat (AGM)
These are a class of VRLA batteries in which the electrolyte is absorbed into a mat of fine glass fibres. Also known as sealed regulated valve, dry cell, non-spillable, and sealed lead acid batteries, they have a greater life span and cycle life than a wet cell battery; they store very well and are the safest, but cost more than wet cells. Popular uses are high performance engine starting (deep cycle), solar power systems, marine, recreational vehicles (RVs), stand-by power, etc.

Gel Cells
These are VRLA batteries with a gelified electrolyte. These are the safest. They store very well, do not sulfate or degrade as easily as wet cells, and have greater resistance to extreme temperatures, shock and vibration. But they cost twice as much as premium wet cells, are very sensitive in terms of adverse reactions to over-voltage charging, and are best used in very deep cycle applications. They are often referred to as sealed lead-acid (SLA) batteries due to their non-leaking containers, but are not completely sealed: the valve regulation system allows gas to be expelled.

Nickel-Cadmium (NiCd) Batteries
These are medium to large, flooded cell batteries, vented and rechargeable. They are designed for harsh environments, extreme temperatures, offer broad performance in any application, and are suited for utility, telecommunications, military and generators. They require less time for charging, can stay idle longer in any state of charge, store well, and can be charged/discharged any number of times without any noticeable damage. They are more superior to lead-acid cells, and generally require less maintenance throughout their service life in regard to the adding of electrolyte or water.

Silver-Zinc Cells
These batteries use the same electrolyte as the nickel-cadmium cell (potassium hydroxide and water), but the anode and cathode differ: the anode is composed of silver oxide and the cathode is made of zinc. They are relatively expensive and can be charged and discharged fewer times than other types of cells. When compared to the lead-acid or nickel-cadmium cells, these disadvantages are outweighed by their light weight, small size and good electrical capacity. They are used to power emergency equipment.

Silver-Cadmium Cells
These batteries combine some of the better features of nickel-cadmium and silver-zinc cells. They have more than twice the shelf life of silver-zinc cells, and can be recharged many more times. Their disadvantages are their high cost and low voltage production. The electrolyte of silver-cadmium cells is potassium hydroxide and water. The anode is silver oxide and cathode is cadmium hydroxide. The different combinations of materials used to form the electrolyte, cathode and anode of different cells provide the cells with different qualities for varied applications.

Combining Cells
In many cases, a battery-powered device may require more electrical energy than what one cell can provide; or it may require a higher voltage or more current, or even both. Under such conditions it is necessary to combine or interconnect a sufficient number of cells to meet the higher requirements. Cells connected in series provide a higher voltage, while cells connected in parallel provide a higher current capacity. To provide adequate power when both voltage and current requirements are greater than the capacity of one cell, a combination of series and parallel network of cells must be used.

Primary Cells
There are many different types of primary cells developed for factors such as cost, size, ease of replacement, and voltage or current needs. Here are some types:
n Manganese dioxide-alkaline-zinc cell: This is similar to the zinc-carbon cell except for the electrolyte used, and offers better voltage stability and longer life. It also has a longer shelf life, and can operate over a wide temperature range. It has a voltage of 1.5V, and is available in a wide range of sizes.
n Magnesium-manganese dioxide cell: This battery uses magnesium as the anode material. It allows a higher output capacity over an extended period of time compared to the zinc-carbon cell. It produces about 2V, and its disadvantage is the production of hydrogen during its operation.
n Lithium-organic/inorganic cell: These two types of battery are high-energy cells. Their main advantages are very high power, operation over a wide temperature range and their light weight, with a long shelf life of up to 20 years. They contain toxic materials under pressure, and should not be punctured, recharged, short-circuited, exposed to excessively high temperatures, incinerated or thrown in trash.

Lifespan
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 normal expansion and contraction of 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 eventually makes 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.

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