If your car is not producing enough electric current, you can check the battery by using a meter reader or volt meter. You could also check the alternator if it is distributing enough power to the car. The alternator is the central nervous system of your car; it is responsible in relaying electrical signals to various specific electronic functions such as the stereo, air-conditioning, the headlights, heater and the windshield wiper. The battery, however, is the blood that provides electricity.
Put on insulated electrical gloves and open the hood of the car. Check all the wires to ensure everything is connected. Open the battery cap and check the wiring connection of the batteries. If there is corrosion in the connection, scrape it clean with a screw driver or any non-conductive material.
Get inside the car and turn on the engine. Turn on the headlights, air conditioning, windshield wipers, stereo and everything you can think of that is electronically run.
Get out of the car and attach the electronic car tester onto the battery. Connect the red wire of the tester to the positive terminal of the battery and the black wire to the negative terminal. Make sure that the voltage reading is around 12V or higher. A 12V reading for a car that is on idle means that your car alternator and electrical charging system is in an acceptable condition.
Inspect the alternator if there are burns. If the insulators are burned, then most likely the alternator wirings are damaged. Depending on the extent of the damage, you may have to replace or rewind it in an auto shop.
