Glossary

Anode
An anode is an electrode through which current enters any nonmetallic conductor. An electrolytic anode is an electrode at which negative ions are discharged, or positive ions are formed, or at which other oxidizing reactions occur. It is the positive electrode of a galvanic cell or an electrolytic capacitor.

Battery
A device that transforms chemical energy into electric energy. The term is usually applied to a group of two or more electric cells connected together electrically. In common usage, the term “battery” is also applied to a single cell, such as a household battery.

Battery Chatter
The temporary loss of battery power when contact between the battery and the battery connectors is lost such as when the device is dropped. Very important in ruggedized PDAs.

Capacitance
The property of a capacitor or an electric circuit that defines its ability to store an electrical charge (or energy) when a given voltage is applied. The international unit of measurement for capacitance is the Farad.

Capacitance, Electrostatic
Capacitance is the ability of a conductor, separated by a dielectric, to store electrostatic charges. The charge Q is directly related to the product of capacitance C and voltage V as in Q = CV. Capacitance is directly proportional to the area of either conductor A (called plates in the parallel-plate capacitor) and indirectly proportional to the distance between the plates d:
C = epsilonA / 4pid, where epsilon is the dielectric constant of the medium between the plates.

Capacitor
A device that stores energy in an electric field by accumulating an internal imbalance of electric charge.

Cathode
The cathode is the electrode through which current leaves any nonmetallic conductor. An electrolytic cathode is an electrode at which positive ions are discharged, or negative ions are formed, or at which other reducing reactions occur. It is the negative electrode of a galvanic cell or an electrolytic capacitor.

Cell
An electrochemical device composed of positive and negative plates, separator, and electrolyte, which is capable of storing electrical energy. When encased in a container and fitted with terminals, it is the basic “building block” of a battery.

Charge
Charge is the conversion of electric energy into chemical energy within the cell or battery. It is achieved by maintaining a unidirectional current in the cell or battery in the direction opposite to that during discharge.

Current
The current in a wire is the quantity of electric charge flowing through a wire in one second. Measured in Amperes (Amps or “A”) or milliamps (mA) for 1/1000 A.

Depth of Discharge (DoD)
The relative amount of energy withdrawn from a battery relative to how much could be withdrawn if the battery were discharged until exhausted.

Discharge
Discharge is the conversion of the chemical energy of the battery into electric energy.

Dielectric
A dielectric is an insulator and a substance that is highly resistant to flow of electric current. Layers of such substances are commonly inserted into capacitors to improve their performance.

Electrolyte
A chemical compound which, when fused or dissolved in certain solvents, usually water, will conduct an electric current. All electrolytes in the fused state or in solution give rise to ions which conduct the electric current.

Electrolytic Capacitor
A capacitor is made up of two parallel plates, the electrodes, with a dielectric between them. The amount of capacitance is directly proportional to the surface area of the electrode and indirectly proportional to the dielectric thickness.

Energy
Output capability (the ability to do work), usually expressed as capacity times voltage, or watt-hours.

Energy Density
The ratio of the energy available from a battery to its volume. The total energy stored in a capacitor is usually quoted in Joules. Traditional capacitors may store a few Joules while supercapacitors store hundreds or thousands of Joules depending on their size.

Equivalent Series Inductance
The amount of inductance in series with an ideal capacitor which exactly duplicates the performance of a real capacitor.

Equivalent Series Resistance (ESR)
The amount of resistance in series with an ideal capacitor which exactly duplicates the performance of a real capacitor.

Fuel Cell
An electrochemical device similar to a battery, but is designed for continuous replenishment of the reactants consumed. It produces electricity from an external fuel supply as opposed to the limited internal energy storage capacity of a battery.

Internal Resistance
The resistance to the flow of an electric current within the cell or battery.

Inductance
The property of a conductor or circuit which resists a change in current flow. It causes current changes to lag behind voltage changes.

Memory Effect
A phenomenon in which a cell, operated in successive cycles to the same, but less than full depth of discharge, temporarily loses the remainder of its capacity at normal voltage levels. This is usually seen only in Nickel-Cadmium cells.

Parallel Connection
The arrangement of cells in a battery made by connecting all positive terminals together and all negative terminals together, so that the voltage of the group is that of one cell and the current drain is divided among the several cells.

Power
The rate at which energy is used, supplied or transferred. It is expressed in WATTs (W). A one-watt source supplies energy at the rate of 1 JOULE per second.

Resistance
Resistance is the potential difference measured between the ends of a conductor when a current is flowing in it. Measured in Ohms (W).

Series Connection
The arrangement of cells in a battery made by connecting the positive terminal of each successive cell to the negative terminal of the next adjacent cell so that their voltages are cumulative.

Supercapacitors
Supercapacitors are high surface area carbon capacitors that use a molecule-thin layer of electrolyte, rather than a manufactured sheet of material, as the dielectric. As the energy stored is inversely proportional to the thickness of the dielectric, these capacitors have an extremely high energy density. They are able to hold a very high charge which can be released in a controlled manner. Also known as Electric Double Layer Capacitors (EDLCs) or ultracapacitors.

Voltage
Voltage is the driving force that pushes electricity through an electrical circuit. A high voltage will push a large amount of electricity or current through a wire. Measured in Volts (V).

Watt
The unit of power, or rate of conveying energy, used in electricity.