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A Primer On Batteries

A battery consists of an energy cell or a group of cells stacked in series for higher voltage or in parallel for higher output current.

The electrical energy of a battery cell is produced by a chemical reaction between its anode, cathode and electrolyte materials. It is worth noting that, in battery terminology, the positive terminal is the cathode, the negative terminal is the anode.

The materials used for the anode, cathode and electrolyte and their quantity, primarily determine the battery's output capacity, specified in ampere-hours (Ah) or watt-hours, (Wh). Other factors, such as energy density (Ah/kg), relative size, cost, thermal stability, storage life, etc., are also a function of the choice of materials. The illustration compares discharge characteristics for several primary battery types. [from The Art of Electronics, 2nd edition, by Paul Horowitz and Winfield Hill, as adapted by the authors from battery literature. Cambridge (UK): Cambridge University Press, 1989.]

Batteries are classified as either primary (non-rechargeable), secondary (rechargable) or reserve (inactive until activated):

  • Primary batteries are often relatively inexpensive; they are usually found in applications where long-term operation with minimal current drain is expected. Examples include a car's miniature, remote activation device for "keyless" entry/alarm, portable hand-held multimeters, portable remote data-loggers, remote or emergency signalling devices, etc. The standard AA, C and D-size dry-cell batteries found in radios, flashlights, toys, etc., are examples of low-cost, consumer-type primary batteries.
  • Secondary batteries have the advantage of being rechargeable; they are often found in applications such as the battery backup in an ac-powered system, (e.g., mainframe computers or emergency lighting systems) where the secondary battery is continuously charged by the system, or in applications where bursts of high-energy output for short periods of time are required, such as in portable power tools.
  • Reserve batteries are designed for very long term storage, and cannot provide any output until a key chemical element (usually the electrolyte) is added. A car's 12 volt battery on the automotive dealer's shelf is an example of a reserve battery.
The following chart lists the most commonly known battery types, and their properties: 

Battery          Type     Anode   Cathode  CellVolts   Ah/kg
Alkaline         Primary    Zn      MNO2       1.5      224
Lithium          Primary    Li      MNO2       3.5      286
Lithium          Primary    Li      SO2        3.1      379
Lead-acid        Secondary  Pb      PbO2       2.1      120
Nickel-
Cad`mium (Ni-Cd) Secondary  Cd      Ni Oxide   1.35     181
Nickel
Metal-Hydride    Secondary  MH      Ni Oxide   1.35     206

Source: Handbook of Batteries, 2nd edition, by David Linden. new York: McGraw-Hill, 1995.