There are two methods of charging of batteries:
1) Constant current method 2) Constant voltage method
1) Constant current method of charging batteries:
In this method, the charging current is kept constant by varying the supply voltage to overcome the increased back emf.
If a charging booster is used the current supplied by it by adjusting its excitation.
It charged on a d.c supply connected in the circuit.
The value of charging current should be so chosen that there is no excessive gassing during final stages of Charging the cell temperature should not exceed 45⁰C.
This method takes a comparatively longer time.
2) Constant voltage charging method of charging batteries:
In this method the charging voltage is held constant throughout the charging process.
The charging current is high in the beginning when the battery is in discharged condition drops off as the battery picks up charge resulting in increased back e.m.f.
This is the common method of charging used in battery shops and in automotive equipment.
In this method time of charging is almost reduced to half.