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Glossary of Battery Definitions

Anode: The electrode where oxidation (loss of electrons) takes place. While discharging, it is the negative electrode; while charging it becomes the positive electrode.

Amps: Also known as Amperes. This is the rate at which electrons flow in a wire. The units are coulombs per second, or since an electron has a charge of 1.602 x 10-19 coulombs, an amp is 6.24 x 10+18 electrons per second. Think of marbles rolling through a tube. If 6.24 x 10+18 pass by in 1 second you wuld have an amp of marbles.

Accumulator: A rechargeable battery or cell (see also Secondary battery).

Amp Hour or Ampere-Hour: One amp hour is equal to a current of one ampere flowing for one hour. Also, 1 amp hour is equal to 1,000 mAh

Aqueous Batteries: Batteries with water-based electrolytes. The electrolyte may not appear to be liquid since it can be absorbed by the battery�s separator.

Actual Capacity or Available Capacity: The total battery capacity, usually expressed in ampere-hours or milliampere-hours, available to perform work. The actual capacity of a particular battery is determined by a number of factors, including the cut-off voltage, discharge rate, temperature and method of charge and the life history of the battery.

Batteries: Two or more electrochemical cells, electrically interconnected, each of which contains two electrodes and an electrolyte. The redox (oxidation-reduction) reactions that occur at these electrodes convert electrochemical energy into electrical energy. In everyday usage, 'battery' is also used to refer to a single cell.

Battery Capacity: The electric output of a cell or battery on a service test delivered before the cell reaches a specified final electrical condition and may be expressed in ampere-hours, watt- hours, or similar units. The capacity in watt-hours is equal to the capacity in ampere-hours multiplied by the battery voltage.

Battery Charger: A device capable of supplying electrical energy to a battery.

Battery-Charge Rate: The current expressed in amperes (A) or milli amps (mA) at which a battery is charged.

Capacity: The total quantity of electricity or total ampere-hours available from a fully charged cell or battery.

Cathode: The electrode where reduction (gain of electrons) takes place. When discharging, it is the positive electrode, when charging, it becomes the negative electrode.

Charge: The conversion of electrical energy, provided in the form of current from an external source, into chemical energy stored at the electrodes of a cell or battery.

Cutoff Voltage, final: The prescribed lower-limit voltage at which battery discharge is considered complete. The cutoff or final voltage is usually chosen so that the maximum useful capacity of the battery is realized. The cutoff voltage varies with the type of battery and the kind of service in which the battery is used. When testing the capacity of a NiMH or NiCD battery a cutoff voltage of 1.0 V is normally used. 0.9V is normally used as the cutoff voltage of an alkaline cell. A device that is designed with too high a cutoff voltage may stop operating while the battery still has significant capacity remaining.

C: Used to signify a charge or discharge rate equal to the capacity of a battery divided by 1 hour. Thus C for a 1600 mAh battery would be 1.6 A, C/5 for the same battery would be 320 mA and C/10 would be 160 mA. Because C is dependent on the capacity of a battery the C rate for batteries of different capacities must also be different.

Cell: An electrochemical device, composed of positive and negative plates and electrolyte, which is capable of storing electrical energy. It is the basic �building block� of a battery

Constant-Current Charge: A charging process in which the current applied to the battery is maintained at a constant value.

Constant-Voltage Charge: A charging process in which the voltage applied to a battery is held at a constant value.

Charge Rate: The amount of current applied to battery during the charging process. This rate is commonly expressed as a fraction of the capacity of the battery. For example, the C/2 or C/5.

Charge cycle: This describes the complete charge and discharge cycle of the battery. Fully draining the battery then recharging it is one charge cycle.

Cycle Life: For rechargeable batteries, the total number of charge/discharge cycles the cell can sustain before it�s capacity is significantly reduced. End of life is usually considered to be reached when the cell or battery delivers only 80% of rated ampere- hour capacity. NiMH batteries typically have a cycle life of 500 cycles, NiCd batteries can have a cycle life of over 1,000 cycles. The cycle of a battery is greatly influenced by the type depth of the cycle (deep or shallow) and the method of recharging. Improper charge cycle cutoff can greatly reduce the cycle life of a battery.

Discharge: The conversion of the chemical energy of a cell into electrical energy, which can then be used to supply power to a system.

Discharge curve: A plot of cell voltage over time into the discharge, at a constant temperature and constant current discharge rate.

Deep Cycle: A cycle in which the discharge is continued until the battery reaches it�s cut-off voltage.

Depth of Discharge: The amount of energy that has been removed from a battery (or battery pack). Usually expressed as a percentage of the total capacity of the battery. For example, 50% depth of discharge means that half of the energy in the battery has been used. 80% DOD means that eighty percent of the energy has been discharged, so the battery now holds only 20% of its full charge.

Discharge, deep: Withdrawal of all electrical energy to the end-point voltage before the cell or battery is recharged.

Discharge, high-rate: Withdrawal of large currents for short intervals of time, usually at a rate that would completely discharge a cell or battery in less than one hour.

Discharge, low-rate: Withdrawal of small currents for long periods of time, usually longer than one hour.

Drain: Withdrawal of current from a cell.

Dry Cell: A primary cell in which the electrolyte is absorbed in a porous medium, or is otherwise restrained from flowing. Common practice limits the term �dry cell� to the Leclanch� cell, which is the common commercial type.

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