If the battery is too low to start an engine, a booster battery connected in parallel with the battery in your car, can supply the needed current to the starting motor. This is not a difficult taks, but it is usually performed in such a manner as to create an unnecessarily hazardous condition. Below are steps on how to do this job.
1. Remove the vent caps from both batteries and place a clean cloth over the openings to prevent contamination of the electrolyte should an explosion ocur.
2. Make sure your eyes are shielded
3. If the booster battery is being used in the electrical system of another vehicle (the most common situation), don’t allow the two vehicles to come into contact with each other.
4. Turn of all electrical equipment in both vehicles other than the ingnition of the car to be started.
5. Connect one end of a jumper cable to the positive (+) terminal of the booster battery. Then connect the other end of the jumper cable to the positive terminal of the dead battery.
6. Connect one end of the second jumper cable to the negative (-) terminal of the booster batttery. Then connect the other end of the jumper cable to the engine block of the car being started. Do not make the second connection to the negative terminal of the dead battery (a very common practice). If you do, you may damage electrical equipment or cause a battery to explode! And keep your face away from the battery while making this connection.
7. Now, it’s time to start the car containing the booster battery. Only then should you start the second car containing the dead battery.
8. When the disabled car is running, first remove the engine-block connection of the negative cable. Then remove the other end of the negative cable.
9. Finally, disconnect the positive cable, being careful not to ground the end of the cable removed first.
One final caution about supplying a battery boost to another vehicle. Never operate your starting motor for more than 30 seconds at a time. Wait a few minutes before operating the starting motor again. This motor draws a heavy current and heats up quickly.