The amount of charge provided by battery is its capacity. Since
charge is the product of current and time , therefore in order to increase
capacity , current should be increased. This is done by connecting more number
of batteries in parallel. This will provide more charge at same terminal
voltage, hence capacity increases.
A household deep cycle 12V (12.6V on fully charged) battery generally contains six 2V batteries in series internally.
Each cell performs electrolysis It has two electrodes , of
lead oxide and other of lead. The electrolyte is a mixture of water and sulphuric
acid.
FULLY DISCHARGED
During complete charging, full amount of sulphuric acid is
left as electrolyte along water. With the help of this electrolyte , movement
of charge takes place between anode and cathode. As discharging begans, the
sulphuric acid starts accumulating over electrodes and at complete discharge only
water is left as electrolyte. Thus transfer of charge stops and we say that
battery is down.
During these processes , some unwanted phenomenon also takes
place which are as follows:
Sulphonation:
During charging there should complete transfer of sulphate
from electrodes to electrolyte but it is not practacally observed. Some amount
of sulphate remains on electrodes . This is sulphonation. It reduces the cross
section area of plate and hences reduces capacity. To avoid this ,
desulphonation process is performed to remove layers of sulphates from
electrodes.
Stratification :
Since water and sulphuric acid both are present in electrolyte
and water is lighter. lighter therefore
after some time sulphuric acid settles down. Due to this, corrosion takes place
in the lower section of electrodes. To avoid this, it is advised to discharge
completely the battery after long cycles or if possible shake the battery
frequently.
Explosion:
Due to over chaging , electrolysis of water takes place and
hydrogen gas is formed. Since it is a supporter of cumbustion and temperature
is also high it explodes.
To avoid this , some ventillations are provided.