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Absorbed Glass Mat (AGM) Battery – Uses a fiberglass-like separator to hold the electrolyte in place. The physical bond between the separator fibers, the lead plates, and the container makes it spill-proof and the most vibration and impact resistant lead-acid battery available today. It uses almost the same voltage set-points as a wet/flooded cell and thus can be used as drop-in replacement for a wet/flooded cell.

Active Material – Compounds (normally applied as a paste) which are active in the battery’s plates. Specifically refers to lead dioxide in the positive plates, and metallic sponge lead in the negative plates. When an electrical circuit is created, these materials react with sulfuric acid during charging and discharging.

Ampere (Amp/A) – The unit of measure of the electron flow rate, or current through a circuit.

Ampere-Hour (Amp.-Hr./ Ah) – A unit of measure for a battery’s electrical storage capacity, obtained by multiplying the current in amperes by the time in hours of discharge. (e.g. A battery which delivers 5 amperes for 20 hours delivers 5 amperes X 20 hours = 100 Amp-Hr of capacity).

Capacity – The ability of a fully-charged battery to deliver a specific quantity of electricity (Amp-Hr/Ah) at a given rate (Amp/A), over a definite period of time (Hr). The capacity of a battery depends on a number of factors such as: active material weight, density of the active material, adhesion of the active material to the grid, number, design and dimensions of the plates, plate spacing, design of separators, specific gravity and quantity of electrolyte, grid alloys, final limiting voltage, discharge rate, temperature, internal and external resistance, age, and life history of the battery.

Cell – The basic electrochemical current-producing unit in a battery, consisting of a set of positive plates, negative plates, electrolyte, separators and case (or container). There are six cells in a 12 volt lead-acid battery.

Circuit – The path followed by a flow of electrons. A closed circuit is a complete path. An open circuit has a broken or disconnected path.

Circuit (Parallel) – Provides more than one path for the flow of current. A parallel arrangement of batteries (usually of like voltages and capacities) has all positive terminals connected to a conductor and all negative terminals connected to another conductor. If two 12 volt batteries of 50 ampere-hour capacity each are connected in parallel, the circuit voltage is 12 volts and the ampere-hour capacity of the combination is 100 ampere-hours.

Circuit (Series) – Only has one path for the flow of current. Batteries arranged in series connect the negative of the first to the positive of the second, the negative of the second to positive of the third, etc. If two 12 volt batteries of 50 ampere-hour capacity each are connected in series, the circuit voltage is equal to the sum of the two battery voltages, (24 volts) and the ampere-hour capacity remains 50 Ah, but at the higher operating voltage.

Cold Crank Ampere (CCA) Rating – The number of amperes a lead acid battery at 0°F (-17.8°C) can deliver for 30 seconds and maintain at least 1.2 volts per cell.

Corrosion – The destructive chemical reaction of a liquid electrolyte with a reactive material — e.g., dilute sulfuric acid on iron, producing corrosion products such as rust. Battery terminals are subject to corrosion if they are not properly maintained.

Current – The rate of flow of electricity, or the movement of electrons along a conductor. It is comparable to the flow of a stream of water. The unit of measure for current is the ampere.

Current (Alternating/AC) – An electrical current that varies periodically in magnitude and direction.  A battery does not deliver alternating current (AC).

Current (Direct/DC) – Current that flows in an electrical circuit of constant magnitude in one direction only. A battery delivers direct current (DC) and must be recharged with direct current in the opposite direction of the discharge.

Cycle – In a battery, one discharge plus one recharge equals one cycle.

Discharging – When a battery is delivering current, it is said to be discharging.

Electrolyte – In a lead-acid cell, a solution of sulfuric acid and water which conducts current through the movement of  ions (charged particles in the electrolyte solution) between positive and negative plates. It supplies sulfate ions for reaction with the active material of both positive and negative plates.

Float charge – Method of charging in which a secondary cell is continuously connected to a constant voltage supply that maintains the cell in a fully charged condition.

Flooded or Wet Cell – Type of battery that uses a liquid electrolyte and can be recharged many times. The most common wet-cell battery is an automobile battery. It is available in two styles: serviceable and maintenance-free.

Forming – In battery manufacturing, formation is the process of charging the battery for the first time. Electrochemically, formation changes the lead oxide paste on the positive grids into lead dioxide and the lead oxide paste on the negative grids to metallic sponge lead.

Gel Cell – Uses essentially the same chemistry as a wet/flooded cell, except that the electrolyte is in gelatin form and absorbed into the plates.

Grid – A lead-alloy framework that supports the active material of a battery plate and conducts current.

Ground – The reference potential of a circuit. In automotive use, the result of attaching one battery cable to the body or frame of a vehicle which is used as a path for completing a circuit in lieu of a direct wire from a component. Today over 99% of automotive and LTV (Limited Terrain Vehicles) applications use the negative terminal of the battery as the ground.

Hydrometer – A device used to determine the state of charge of a battery by measuring the specific gravity or density of the electrolyte (i.e., the concentration of sulfuric acid in the electrolyte).

Lead-Acid battery – An electrical storage device that uses a reversible chemical reaction to store energy. It uses a combination of lead plates or grids and electrolyte, consisting of diluted sulfuric acid and water to convert electrical energy into potential chemical energy and back again.

Load Tester – An instrument which draws current from (discharges) a battery using an electrical load while measuring voltage. It determines the battery’s ability to perform under actual discharge conditions.

Low-Water-Loss Battery – A battery which does not require periodic water addition under normal driving conditions; also referred to as maintenance-free battery.

Negative – Designating, or pertaining to, electrical potential. The negative battery terminal is the point on a battery from which electrons flow during discharge.

Ohm – A unit for measuring electrical resistance or impedance within an electrical circuit.

Ohm’s Law – Expresses the relationship between volts (V) and amperes (A) in an electrical circuit with resistance (R). It can be expressed as follows: V = IR Volts (V) = Amperes (I) x Ohms (R). If any two of the three values are known, the third value can be calculated using this equation.

Open Circuit Voltage – The voltage of a battery when it is not delivering or receiving power (and has been off-power for 4-6 hours). It is 2.11 volts for a fully charged battery cell, or 12.66 for a fully charged 12 volt battery. (6.33 for a 6 volt battery.)

Positive – Designating or pertaining to a kind of electrical potential -opposite of negative. A point or terminal on a battery having higher relative electrical potential.

Power – The product of voltage and current, measured in watts.

Primary Battery – This type of battery can store and deliver electrical energy but cannot be recharged.

Reserve Capacity Rating – The time in minutes that a new, fully-charged battery will deliver 25 amperes at 80°F and maintain a terminal voltage equal to, or higher than, 1.75 volts per cell. This rating represents the time the battery will continue to operate essential accessories if the alternator or generator of a vehicle fails.

Resistance (Electrical) ­– The opposition to the free flow of current in a circuit. It is measured in Ohms.

Secondary Battery – A battery which can store and deliver electrical energy and can be recharged by passing direct current through it in a direction opposite to that of discharge.

Separator – A divider between the positive and negative plates of an element which prevents them from shorting, and allows the flow of current to pass through. They are made from numerous materials such as: polyethylene, polyvinyl chloride, rubber, glass fiber, and cellulose.

Short Circuit – Unintended current-bypass in an electric device or wiring, generally very low in resistance and thus causing a large current to flow. In a battery, a cell short circuit may be permanent enough to discharge the cell and render the battery useless.

Specific Gravity (SG) – The density of a liquid compared to the density of water. The specific gravity of the electrolyte is the weight of the electrolyte compared to the weight of an equal volume of pure water.

State of Charge – The amount of electrical energy stored in a battery at a given time, expressed as a percentage of the energy when fully charged.

Sulfation – Formation of lead sulfate crystals on the plates of a lead acid battery.

Volt – The unit of measure for electrical potential.

Voltage – Electric potential expressed in volts.

Voltage Drop – The net difference in the electrical potential (voltage) when measured across a resistance or impedance (ohms). Its relationship to current is described in Ohm’s law.

Watt – The unit for measuring electrical power, i.e., the rate of doing work, in moving electrons by, or against, an electrical potential. Formula: Watts = Amperes x Volts.

Watt-Hour (Watt-Hr, WH) – The unit of measure for electrical energy expressed as Watts x Hours.

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