The car battery is one of the main electrical components of a vehicle. It must be maintained regularly in order to allow the car to function properly and enhance the battery's life cycle. It is normal for a battery to be charged at regular intervals, and though this is normally done by your car's engine during regular use (or by another vehicle in an emergency), you can also build your own battery charger to use as an external charging system when needed.
Acquire a power source with a voltage equal to the car's battery voltage. A typical car battery is 12 volts, thus a 12-volt DC power adaptor will be sufficient to charge this battery.
Cut the connector end of the adaptor cable and strip the cable of about an inch of insulation with the electrical pliers.
Split the two wires by pulling them apart until each wire is separated from the other by about a foot.
Connect one wire to the red alligator clip by soldering the wire to the alligator clip terminal. Repeat the procedure for the second wire and black alligator clip.
To charge the battery, simply connect the alligator clips to their appropriate positive or negative terminals and plug in the power adaptor.
Make sure the DC power adaptor is of the same voltage as the car battery, otherwise it will not be powerful enough to charge the battery.
Avoid getting the battery too hot during charge. Use caution when manipulating the soldering iron to avoid hazards.