An automotive battery is a type of rechargeable battery that supplies electric energy to an automobile. An automotive SLI battery (starting, lighting, ignition) is an automotive battery that powers the starter motor, the lights, and the ignition system of a vehicle's engine, mainly in combustion vehicles.
Automotive SLI batteries are usually lead-acid type (electric cars may also use in addition to non-lead batteries), and are made of six galvanic cells connected in series to provide a nominally 12-volt system. Each cell provides 2.1 volts for a total of 12.6 volts at full charge. Heavy vehicles, such as highway trucks or tractors, often equipped with diesel engines, may have two batteries in series for a 24-volt system or may have series-parallel groups of batteries supplying 24 V.
Lead-acid batteries are made up of plates of lead and separate plates of lead dioxide, which are submerged into an electrolyte solution of about 38% sulfuric acid and 62% water. This causes a chemical reaction that releases electrons, allowing them to flow through conductors to produce electricity.
As the battery discharges, the acid of the electrolyte reacts with the materials of the plates, changing their surface to lead sulfate. When the battery is recharged, the chemical reaction is reversed: the lead sulfate reforms into lead dioxide and lead with the sulfate returning to the electrolyte solution restoring the electrolyte specific gravity.
Lead-acid batteries for automotive use are made with slightly different construction techniques, depending on the application of the battery. The "flooded cell" type, indicating liquid electrolyte, is typically inexpensive and long-lasting, but requires more maintenance and can spill or leak. Some flooded batteries have removable caps that allow the electrolyte to be tested and electrolyte level maintained.
More costly alternatives to flooded batteries are valve regulated lead acid (VRLA) batteries, also called "sealed" batteries. The absorbed glass mat (AGM) type uses a glass mat separator, and a "gel cell" uses fine powder to absorb and immobilize the sulfuric acid electrolyte. These batteries are not serviceable: the cells are sealed so the degree of charge cannot be measured by hydrometer and the electrolyte cannot be replenished.
They are typically termed "maintenance-free" by proponents, or "unable to be maintained" by skeptics. In particular, they are not suitable for older (pre-alternator) vehicles with unsophisticated charging control systems. Both types of sealed batteries may be used in vehicular applications where leakage or ventilation for vented gasses is a concern.
The starting (cranking) or shallow cycle type is designed to deliver large bursts of current for a short time, which is needed to start an engine. Once the engine starts, the battery is recharged by the engine-driven charging system. Starting batteries are intended to have a low depth of discharge on each use. They are constructed of many thin plates with thin separators between the plates, and may have a higher specific gravity electrolyte to reduce internal resistance.
The deep cycle (or motive) type is designed to continuously provide power for long periods of time (for example in a trolling motor for a small boat, auxiliary power for a recreational vehicle, or traction power for a golf cart or other battery electric vehicle).
They can also be used to store energy from a photovoltaic array or a small wind turbine. Deep-cycle batteries have fewer, thicker plates and are intended to have a greater depth of discharge on each cycle, but will not provide as high a current on heavy loads. The thicker plates survive a higher number of charge/discharge cycles. The specific energy is in the range of 30-40 watt-hours per kilogram.
Some tutorial video to help us enlighten and give us a clear understanding of how automotive battery, starting and charging system work.
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