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| Q: |
What exactly
is a battery? |
| A: |
A
battery is a source of
electrical energy. Its
smallest unit is called
a (galvanic) cell. A battery
usually consists of several
individual cells electrically
connected in series. The
chemical energy as stored
in each cell is converted
directly into electrical
energy when its terminals
are connected to an electrical
consumer.
The
battery can thus be considered
as an electrochemical
energy conversion system,
similar to the internal
combustion engine. The
internal combustion engine
converts chemical energy
into mechanical energy.
To do this, two substances
are required: fuel and
oxygen. A galvanic cell
also needs two substances
for energy conversion,
represented by two electrochemically
active electrodes of different
compositions, both of
which are immersed in
an electrolyte which provides
a conductive medium between
them.
One
of the electrodes uses
a metal such as lead.
Within the electrolyte,
it establishes a negative
potential and consequently
represents the negative
electrode. The other electrode
comprises an electron
conducting compound rich
in oxygen, lead dioxide
in combination with a
suitable oxygen electrode.
This electrode establishes
a positive potential within
the electrolyte and consequently
represents the positive
electrode of the electrochemical
system. Depending on the
electrochemical system,
the cell voltage will
be 2 V. When connecting
the system to an external
load, electrical energy
will be taken out of the
system, while the chemical
energy stored inside the
cell or battery will be
used up.
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| Q: |
Why do batteries have different voltages
and capacities? |
| A: |
Different
devices operate at different
voltages and power levels.
They all require batteries
that provide the necessary
power output at a minimum
discharging voltage. The
voltage of a given battery
depends on the number of
single cells connected in
series and on their electrochemical
system. For instance, a
lithium-manganese-dioxide
cell has a nominal voltage
of 3 V, a rechargeable lead-acid
cell offers 2 V, while an
alkaline-manganese cell
has an initial voltage of
approx. 1.5 V, that decreases
during discharge to 0.9
V and below.
The
capacity of a battery
is determined by the amount
of chemical energy stored
inside its housing. It
determines - for a given
current of a given device
- the service life of
the battery.
In
order to properly operate
a specific electrical
device,
- the
battery's operating
voltage must be matched
to that of the device;
- the
correct battery capacity
must be selected in
order to provide the
necessary operating
time for the device;
- the
battery must be able
to deliver the power
required: its internal
resistance must be smaller
than that of the device.
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| Q: |
Which voltages are
typical for which types
of batteries? |
| A: |
| Battery Type |
Voltage |
Most
Common Applications |
| SLI-battery
(starter battery)
|
12V,
6V |
Automobiles,
commercial vehicles,
motorcycles |
| Semi-traction, traction battery
|
12V, 24V
48V
|
Electric vehicles,
wheel-chairs, lawnmowers,
boats, house trailers,
cleaning equipment,
solar technology |
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| Q: |
How long may batteries be stored idle? |
| A: |
In
principle, no battery
can be stored without
loss of energy, although
some battery systems may
be stored for longer periods
of time than others. Processes
inherent to the battery's
electrochemical system
cause a gradual, but unavoidable
loss of usable energy
which, however, is predictable.
The best known process
is "self-discharge". This
generally has to do with
the electrolytic solubility
of the positive electrode
material or its thermodynamic
instability (e.g. spontaneous
decomposition).
Self-discharge
in rechargeable batteries
(secondary batteries,
accumulators) is particularly
high in comparison to
primary batteries. At
room temperature the rate
of self-discharge is in
the range of 15% to 25%
per month, depending on
the system. Of the rechargeable
systems, solar batteries
have an unusually low
self-discharge rate of
only 10% per month.
Electrochemical
self-discharge in primary
batteries is considerably
lower, and may even be
below 2% per year at room
temperature. However,
various processes take
place in parallel with
this which lead to an
increase of the battery's
internal resistance during
storage. These processes
lead to a reduction in
load capability. Loss
of usable energy becomes
noticeable only at relaes
(e.g. motor applications,
flashlights etc.). This
effect, however, has nothing
to do wittively high discharge
rath self-discharge. At
low discharge rates the
increased internal resistance
which occurred during
storage will not be detectable.
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| Q: |
What is the best way to store batteries? |
| A: |
A general rule is: The higher the storage
temperature, the worse the
capacity retention and vice
versa. A refrigerator, with
a temperature range from
0°C to 10°C, is a good place
for storing batteries, especially
primary batteries. The refrigerator
may, of course, also be
used to store secondary
batteries, but since they
are rechargeable, their
loss of capacity during
storage may be better compensated
by recharging, particularly
as they can take up substantial
space in the refrigerator
(e.g. automotive batteries) |
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| Q: |
What consequences can a battery short
circuit have? |
| A: |
An
"external short circuit"
can occur if the external
terminals of a battery
are bridged by any kind
of conducting material.
Depending on the battery
system, a short circuit
may have serious consequences.
For example, the temperature
of the electrolyte may
rise, thus building up
an internal gas pressure
which may open the pressure
valve of the battery and
eject electrolyte from
the battery. This can
cause injuries. In extreme
cases a detonation may
even occur if the safety
vent fails to respond
(due to e.g. a molding
defect during production).
It is also important to avoid mechanical
impacts which could deform
the battery and result
in internal electrode
short circuits with the
consequences described
about. |
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| Q: |
How do I know when to test/replace
my battery? |
| A: |
You may need to test/replace
your battery if:
1) Your starter motor is
experiencing slow or interrupted
turnover;
2) Your instrument panel
indicates battery discharge
for extended periods after
the engine is running;
3) Your battery seems to
lose power quickly in cold
or extended starts; or,
4) Your headlights dim at
idle.
Any of these warning signals
may also indicate a problem
with the electrical system
in your vehicle and not
necessarily a battery failure.
If you suspect that your
battery is failing, have
it tested or replaced as
soon as possible. |
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