This is 12V Car Battery Charger simple circuit. This circuit is designed to solve some problems that occurs in most car battery chargers. The problem that occur in most car battery chargers is when the charger is not turned off, the battery will overcharge, the plate of the  charger will destroyed and the electrolyte of the charger will lost because of evaporation. This circuit will monitor the charge condition of the battery by using a closed loop control circuit. A high charge current is applied until the battery is completely charged. Here is the schematic diagram of the  circuit:

12V Car Battery Charger circuit schematicThe red LED will turn on, when charging is complete and charging circuit will deactivated. This circuit used only for 12 V battery. When wiring up the circuit, Certain emphasis should be taken. They are hose supplying current to the battery being charged and the connections of the transformer to the circuit board. To prevent heat build-up and voltage-drop when current flows through the circuit, the connections of the transformer to the circuit board should be made with cables having a large cross-sectional area. [Source: Sam Electronic Circuit]