What is a battery?
The word battery means a collection, as in Gun Battery. An electric battery consists of two or more Galvanic cells.
A Galvanic cell is an
electrochemical system that transforms chemical energy into electric energy.
Such a cell in speaking terms is called a battery.
purpose is to store energy and when needed release this energy in the
form of electric energy. The amount of energy a battery can release is
synonymous with its capacity. The term energy is rated in joule (j). However,
electrical energy is often represented in Wh (Watt Hours). As a battery’s
voltage is somewhat constant its capacity is a function of current × time (Ah).
Non-chargeable batteries are called primary batteries.
Batteries used in an ordinary flashlight are usually primary batteries.
Rechargeable batteries are called secondary batteries
and consist of electrolytic cells capable in generating chemical energy
into electrical energy. An ordinary car battery is a secondary battery
also called accumulator.
A Fuel cell is not a galvanic cell. However, it is constructed
in a similar way and can generate electric current. A fuel cell transforms
hydrogen and oxygen gas into water. This reaction generates 0.7 Volt.
A battery can consist of a group of batteries. An example
is a battery in an UPS that contains 32 serial connected 12 Volt batteries
each including 6 cells of lead-acid type. Each cell generates 2 Volt resulting
in a 36*6*2=384 Volt battery. Our 12 Volt battery in the example above
is sometimes referred to as a battery block or simply a block.
While a battery’s total voltage is the sum of each
individual cell’s voltage its current is limited to that of the
weakest cell. Therefore, if a short circuit in one 2 Volt cell total voltage
would fall from 384V to 382V i.e. only 0.5%. Yet, total capacity falls
to the same level.
Reliability and life cycle.
In each cell
there is an ongoing chemical process. Some of these processes are necessary
while others are harmful resulting in a decrease of the cell's capacity.
Chemical reactions in a cell are affected by internal factors such as
impurities in the electrolyte and external factors such as recharge voltage,
recharge current, temperature and humidity.
Furthermore, a cell’s aging process is affected by historical facts such as numbers and characteristics of recharge and discharge. After a period of time some cells will be deteriorated.
Common symptoms in failing batteries
- Corroding battery plates
- Expansion of battery plates
- Sulfur coating on battery plates
- Reversed Polarity
- Short Circuit
- Open Circuit
- Dry out
The Car Battery FAQ http://www.batteryfaq.org/