1 Connect the positive (usually red) charger cable to the positive (+) battery terminal and the negative (usually black) cable to the negative (-) battery terminal. 2  Decide whether you want to charge the battery slowly (trickle charge) or quickly. Use the correct charger for your particular car battery. 2  Check the car owner's manual for information (or ask your car dealer or trusted auto mechanic). 3  Read the charger manual and make sure you understand how the charger works and what precautions are necessary. 4  Pay close attention to all the warnings.