Deep Cylce Batteries
The basic rule of conserving energy states that the total amount of energy in a system remains constant. It states that energy cannot be destroyed. Energy however, can change form. For instance, the chemical energy stored within a rock pushed up a hill (from a person/machine pushing the rock) is converted to potential energy, which is then converted into kinetic and thermal energy when the rock rolls down the hill. Just like the rock that sits atop the hill, a battery is an electrical storage device that is used to store electricity. The battery backup that stores this electricity is not converted 100% into electricity when it is used, as energy released can be lost as well as thermal energy. For a battery power backup device, there is a need to charge it with more power than its output to fully re-charge it.
There are different types of batteries. Battery power backup types are classified under two category types, application type (automotive, marine, and deep-cycle) or construction type (flooded (wet), gelled, and AGM (Absorbed Glass Mat)). A deep-cycle battery is designed to provide consistent voltage as the battery backup device discharges. A true deep cycle battery will have solid lead plates, which are also thicker and are designed to discharge right down to 80% per discharge.
Automotive batteries (or starting, lighting and ignition (SLI) batteries) which make up most starter batteries (provides current for starting internal combustion engines), are designed to deliver energy spikes to literally 'jump-start' an engine, just like how a fibrilator helps jump start a heart. Automotive batteries are typically designed with thin and porous sponge-like plates for maximum surface area storage of these burst of electrical energy. Marine batteries are hybrids between the deep-cycle and automotive.
The types of battery power backup devices are further divided according to their construction, namely Flooded, Gel, and AGM. Flooded (also known as Wet Cells) are common lead-acid battery backup devices used today. Wet cell marine batteries are not sealed (they can be accessed via a half inch hole on the top casing) so that the electrolytes can be replenished while charging the battery. The battery is made of one or more flooded cells with a grid of lead plates and an electrolyte (sulfuric acid). Special care must be given to ensure that the electrolyte does not come into contact with the user or saline water because the device is not sealed. Wet cell batteries are commonly used in large backup power supplies for telephone and computer centers, grid energy storage, and off-grid household electric power systems. Lead-acid batteries are also used in a heating filament (with 2 to 12 volts) in early vacuum tube (valve) radio receivers, emergency lighting in case of power failure, and large lead-acid batteries are used to power the electric motors in diesel-electric submarines as well as nuclear submarines.
Another type of battery is Gel Cells which utilize thickening agents like fumed silica to immobilize the electrolyte. Because gel cells are sealed and cannot be re-filled with electrolyte, the rate of re-charge must be carefully controlled. The gel cells use a lower charging voltage than flooded cells, thus take a longer time to be fully re-charged. The cells should not be overcharged either, as that would create voids and cause the battery capacity to go down. Gel batteries are battery power backup for alarms, smaller computer systems (where uninterruptible power supply is needed), electric scooters, electrified bicycles and marine applications.
The third type, Absorbed Glass Mat (AGM) uses a fiberglass like separator to hold the electrolyte in place. Because the electrolyte (acid) is contained in the fiberglass mats, they cannot spill, even if broken. This also makes the battery vibration and impact resistant. AGM batteries can also be held in storage without the need to be re-charged for long periods of time. AGM cells are used in battery electric vehicles, as well as instances where there is a high risk of the battery being laid on its side or over-turned, like with motorcycles.
Batteries with higher or faster rate of discharge are said to be less efficient than slow discharge batteries. A fast discharge rate can cause loss of energy, such as dissipation due to heat. This loss of energy is due to the batteries internal resistance. The lower the internal resistance, the better the battery is. Deep cycle batteries are lead-acid batteries, which have an efficiency of 85-95% discharge rate. This is the type of battery that flooded gel and AGM cells are made of with the only variation being the construction of the plates.
So how long does a battery last? This depends on the way it was charged, maintained, storage temperature and how the battery is being used. An automotive battery can last between 3 to 12 months, while a deep-cycle battery can last any where between 4 to 8 years. A marine battery may last up to 6 years.
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