The charging current is controlled by the current control circuit. General-purpose 3 terminal voltage regulator is used for control of voltage and current.
This project is not so important for those who ride a car every day. In my case, a car is not used every day. In that case, the voltage of a battery is falling and a car sometimes cannot be put into operation.
If the battery itself is left for a long period of time, the electricity of it will be lost by natural electric discharge. Furthermore, in the case of the latest car, various kinds of electric devices are always backed up more often with a battery. Therefore, even when the car is not being used, the electricity of a battery is consumed little-by-little.
http://www.hobby-elec.org/e_car2.htm
