USEFUL INFORMATION
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Glossary of Battery Terms: Technical and commonly used terms to specify and define batteries.
AGM BATTERY: The acronym for “Absorbed Glass Mat” used to describe sealed lead-acid batteries that employ an absorbent fiberglass material to hold the electrolyte in place so the battery can be used in any position.
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AMP-HOURS: A term used to specify the capacity of a fully charged battery. It is the constant current in amperes multiplied by the time in hours the current is drawn down to a specified voltage, often referred to as the “cutoff voltage”. Temperature is a factor and is normally 20°C (68°F) when determining the amp-hour capacity.
Typically, for lead-acid batteries the cutoff voltage is 1.75 volts per cell. For a 6-volt lead acid battery with 3 cells the cutoff is 5.25 volts. Likewise in a 12-volt, 6 cell battery it is 10.5 volts.
Commonly used discharge times are 6, 8, and 20 hours.
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An example of amp-hour (Ah) battery capacity is as follows: A fully charged 12 volt battery that can provide a constant 10 amperes of current for 20 hours is said to have a capacity of 200Ah, at the 20 hour rate, (to a cutoff voltage of 10.5 volts measured at a temperature of 20 degrees C). Shorthand for showing this capacity is 200Ah at C20.
When a battery discharges at a constant rate, its capacity changes according to the amperage load. In the example above, capacity increases when the discharge current is less than the 20-hour rate and decreases when the current is higher. Likewise the rate of discharge increases when the time period is less than 20-hours and decreases when the time period is longer.
BATTERY: A device for storing chemical energy and converting and discharging this energy as electrical current.
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CAPACITY: The ampere-hours available from a cell or battery. (see amp-hours)
• Discharge Capacity-The ampere-hours, which may be obtained from a fully charged cell or battery during discharge.
• Rated Capacity (C)-The discharge capacity in ampere-hours, which a manufacturer specifies may be obtained from a cell or battery at a given constant discharge current, time and temperature (see Amp-Hours).
CELL: An electrochemical system, which converts chemical energy into electrical energy. The voltage of a cell depends on the combination of chemicals of which it is comprised (often referred to as battery or cell chemistry).
• Cell reversal-The act of reversing the polarity of a cell, i.e. by excessive discharge.
• Primary Cell-An electrochemical device which can only be discharged and not recharged.
• Secondary or Storage Cell- A reversible electrochemical system, which may be discharged and recharged a number of times.
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CHARGE: The conversion of electrical energy to chemical energy in a cell or battery.
• Charge Equalization-A method of using increased charging voltage to bring all of the cells in battery to the same state of charge. Typically used in stationary, standby batteries that are infrequently discharged and under a prolonged maintenance charge (see float charge).
• Charge Voltage-The voltage applied to a cell during charging.
• Charging Temperature Coefficient-The factor by which the charging voltage must be adjusted for a given change in temperature.
• Constant Current Charge- A method of charging a cell by applying a non-varying current.
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• Constant Voltage Charge- A method of charging a cell by applying a non-varying voltage.
• End of Charge- The point at which a target voltage is reached and the charge is terminated.
• Float Charge- A maintenance charge of relatively low amperage that is commonly used in stationary, standby battery applications where the battery is infrequently discharged.
• Overcharge- The charge put into a cell in excess of that needed to return the cell to full capacity. Can lead to cell damage.
• Pulse Charge-A method of cycling the rate of charging at a high frequency that is claimed to reverse battery deterioration from “sulfation”.
• Taper-Current Charge- A method of charging the cell by applying a current that is gradually reduced as the voltage of the cell increases during charging.
• Trickle Current Charge- A method of method of maintaining the capacity of a cell by a small constant current to the cell (another description of float charge).
• State of Charge- The remaining capacity of a cell as compared to the rated capacity.
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CYCLE: Discharging a fully charged battery and then recharging.
DISCHARGE: The conversion of chemical energy in a cell or battery to electrical energy.
• Depth of Discharge- The percent of rated capacity removed from a cell or battery during discharge.
• Discharge Rate- The amount of current being withdrawn from a cell or battery. Can be expressed as a fraction or percent of the rated ampere-hour rating.
• Pulse Discharge-A non-continuous discharge.
• Self-Discharge-Conversion (loss of capacity) of the active materials in a cell on open circuit from a charged to discharged state.
• Self-Discharge Rate- The percent of capacity lost in a cell on open circuit over a specified period of time.
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ELECTRODE: A conducting mass containing materials, which are capable of reacting with the electrolyte in a cell to produce or accept current.
ELECTROLYTE: The material in a cell that transfers electrons between the electrodes. Depending on type and chemistry of the cell, the electrolyte may be a solution or solid and may change composition or remain constant during operation.
ELECTROLYSIS: The electrochemical decomposition of water from the electrolyte.
GEL CELL: A type of sealed lead-acid cell or battery in which the electrolyte is mixed with a solidifying additive that holds the electrolyte in place allowing the cell or battery to be used in any position.
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GRID: The current collector portion of the electrode.
INTERNAL RESISTANCE OR IMPEDANCE: The apparent change in voltage as a function of current caused by resistive and polarization effects within a cell. Used to determine the capacity and condition of a cell.
MAINTENANCE-FREE: A term used for describing a type of cell or battery, which may be operated without the addition of water during its recommended life.
MEMORY EFFECT: A phenomenon seen in nickel cadmium batteries where only the capacity demanded of it during previous cycles is delivered. It is experienced in small sealed nickel cadmium and not in larger vented stationary cells. Completely discharging of the cell followed by recharging should bring a good cell back to its rated capacity.
OUTGASSING: The release of gas from a cell or battery during operation.
POTASSIUM HYDROXIDE: A solid chemical that is dissolved in water to make the alkaline electrolyte solution used with nickel cadmium cells.
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RECOMBINATION: A design used in sealed batteries where oxygen produced at the positive electrode during charging is absorbed at the negative electrode with hydrogen to produce water, preventing over pressure and drying out of the battery.
SEPARATOR: The material used to isolate the positive from the negative electrode or plate in a cell.
SULFATION: A term used to describe deterioration in a lead-acid cell in which a portion or all of the active material will not chemically react during charging and store chemical energy. The battery is said to be sulfated.
SULFURIC ACID: Diluted with water to a typical specific gravity of 1.265, it is the electrolyte used in lead-acid batteries.
SVRLA: The acronym for Sealed Valve Regulated Lead-Acid battery in which GEL or AGM designs along with recombination are used to produce a sealed, maintenance-free battery that is fitted with a valve device to vent gases should an over pressure develop during operation.
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VOLTAGE:
• Equalization Voltage- the manufacturer's recommended over voltage that is applied to bring all the cells in a battery up to full and equivalent state of charge.
• Float Voltage- Used in standby power applications where the battery or cell is infrequently discharged, it is the constant voltage recommended by the manufacturer and applied to maintain optimum capacity and life expectancy.
• Nominal Voltage- The average voltage of a cell or battery.
• Open Circuit Voltage- The no load voltage of a cell or battery.
• Over-Voltage- The difference between the measured and equilibrium voltage of a cell or battery.
WATT HOURS: A way of expressing the capacity in terms of energy in a cell.
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