Here is a simple and easy to build circuit diagram of a 12V car battery charger:

The above circuit claimed have ability to prevent battery overcharge that make electrolyte lost due to evaporation. This circuit will eliminate the problems by monitoring the battery’s condition of charge through its retroactive control circuit by applying a high charge current until the battery is completely charged. When charging is complete, it turns on the red LED (LD2) and deactivates the charging circuit.

This is a variable power supply controlled with PIC microcontroller. There is LCD display in this circuit which will show the actual value of power supply output. This power supply use push on switch to adjust the output voltage and current value.

Schematic Diagram:

Component List:
C1 = 2000uF per AMP, 40V (adjust capacity to power supply amps)
C2,C3,C12,C15,C18,C21 = 0.1uF CER
C4 = 0.01uF CER
C5A,C5B,C5C,C5D = 0.01uF CER
C6,C7 = 0.05uF CER
C8 = Not used
C9,C11,C19,C20 = 1uF CER
C10 = 470uF 15V EL RADIAL
C13 = 4.7µF 50V EL RADIAL
C14 = 0.001uF CER
C16,C17 = 22pF CER

This battery charger circuit is used for rechargable lithium battery.

Charging is accomplished with a constant current of 60 mA for AA cells to a cutoff of 2.4V per cell, at which point the charge must be terminated.