A battery releases electromotive force (EMF) to induce an electric current in a circuit by transferring electrical energy from the chemical energy stored within it through electrochemical reactions between its electrodes and electrolytes. Batteries come in wet and dry forms, with wet cells using a liquid electrolyte while dry cells use paste, and rechargeable secondary batteries can be recharged by applying electric current to reverse the chemical reactions unlike disposable primary batteries. The water level in lead-acid batteries should be topped up after charging to the designated level.

1. Energy & Environment

2. For electricity to flow, there has to be
something to push the electrons along. EMF
This is called an electromotive
force (EMF)
EMF is measured in volts
A battery releases EMF to a circuit which
induces current.
A battery is a group of cells which
transfer electrical energy from
chemical energy

3. Because of the Electrochemical
way a battery Device
works, the power
supply is DC -
-
Chemical energy Electrical energy
Chemical reaction
between electrodes Creates a voltage
& electrolytes

4. Number of electrons = Number of protons
29-18=11 29-36=-7 -ve charge as
Cu 11+
+ve charge as electrons been
Cu 7-
electrons gained.
been lost.
29x Protons
18x Electrons 29x Protons
36x Electrons

5. Other cells are
Example of a Wet made this way
Cell using different
electrodes and
electrolytes
Electrochemical
Device
+
- Sulphuric acid Hydrogen &
Zinc Sulphate Ions
Copper
Negative ions Positive ions
(lots of electrons) (missing electrons)

6. Zn Zn
Normally zinc contains many impurities
e.g. copper & iron Zn
Zn
These react with the zinc like the carbon Fe
Zn
electrode Cu
This takes ions away from the current Zn
Zn
and electrical power is lost.
Fe Zn
This is minimised by coating the
electrode in mercury or use pure zinc Zn
without impurities
Zn
Cu
Zn Zn Zn Zn
Zn Zn
Zn Zn
Fe Zn
Zn Zn
Cu
Zn Zn Zn Zinc
Zn
Fe Zn Zn Zn
Zn Zn
Cu Zn Zn Zn

7. Cu
H
Cu
Hydrogen ions are produced in the Cu
chemical reaction between the electrodes Cu
and electrolyte Cu
Cu
Cu
Because of its charge it is attracted to the Cu
H
copper electrode Cu
Cu
H
H
Cu Cu
Hydrogen is a bad conductor of electricity. H
This increases the resistance of the copper
electrode.

8. H
H
H
H
This can eventually stop
the flow of electrons H
This is called polarization
This can be reduced by using a depolarizer which converts the
H back into H2O. Or the rods can be cleaned with a brush.

9. Electrolyte is a paste Positive electrode
rather than liquid.
Unlike a wet cell the
Negative electrode
battery can work in
any position
Electrolyte Ammonium
Suitable for small
portable devices chloride
Manganese
oxide

10. Do you think a potato
can act like a
battery?
How could we
increase the voltage
of this circuit?

11. Disposable batteries
Used once and thrown away
Used in:
Portable device Devices away Devices only
with low current from a power used
source sometimes
Primary cells cannot be recharged as the chemical reactions are
not easily reversible

12. Rechargeable batteries
Must be charged before use
Recharged by applying electric current, which reverses the
chemical reactions that occur during its use
The oldest form of rechargeable
battery is the lead-acid battery
It is a wet cell so must be kept
upright and ventilated
Heavy & Big
Low cost
Used as car
High current
batteries

13. Made up of a series of identical cells each
containing sets of positive and negative
plates
The voltage of lead acid cell
is normally 2 volts
So for a car battery that needs
12volts 6 cells are added in
series and encased in a plastic
box

14. Should never run flat. Charge when 25% of charge left
Should regularly be charged even if not is use. The internal
resistance will cause it to discharge
A battery can go completely flat without ever having been put
into service
A battery should never be stored
directly on the ground or on concrete.
A wooden pallet is best as it does not
conduct or allow damp paths but does
allow good air circulation

15. Fully Charged + -
1. The colors of the positive & negative plates become dark
brown & grey respectively
2. The electrolyte has a relative density of 1.25 to 1.30
3. Plates form of bubbles
4. The EMF or a cell is 2.0 volts
Uncharged
1. -
+ plates become
The colors of the positive & negative
white due to formation of lead sulphate.
2. The electrolyte becomes dilute & its relative density lies
below 1.18.
3. The e.m.f. of the cell becomes 1.8 volts.

16. The plates of flooded batteries must always be fully submerged
in electrolyte.
Fill battery with distilled or de-ionized water to cover the plates
if low. Never add electrolyte.
The frequency of watering depends on usage, charge method and
operating temperature
A new battery should be checked every few weeks to determine
the watering need
Fill water level to designated level after
charging. Overfilling when the battery is
empty can cause acid spillage.

17. Charge in a well-ventilated area. Hydrogen gas generated during
charging is explosive.
Do not charge at temperatures above 49°C (120°F).
Over charging is bad for the battery
Although batteries can be recharged, deterioration
occurs after each cycle

18. Now the hydrometer floats
Once squeezed this results in a in the acid. The density of
vacuum in the glass tube. the acid can then be read
on the floating hydrometer
Acid is then pushed
into the glass tube
due to atmospheric
pressure.
When the battery is fully charged the cell should have a relative density of
1.25 to 1.30.
A reading of less than 1.18 means that recharging is necessary

19. Batteries can be very dangerous if not used correctly e.g.
Recharging a primary battery
Short circuiting a battery
When a battery is recharged at an
excessive rate
Overcharging
Disposing of a battery in fire

20. EMF
1. What is EMF?
2. What type of energy is stored in a battery?
What type of energy is this transferred to?
3. What is the difference between a wet and
dry cell?
4. What can you do to a secondary battery
that you cannot do to a primary battery?
5. Should you top up the water of a lead acid
battery before or after charging?