A car battery contains chemicals that produce hydrogen gas during use. Hydrogen gas is volatile and has been known to explode under certain conditions, causing serious injuries. For example, a car battery may explode while starting the car, while jump starting or by carelessly shorting the terminals with a screwdriver. In fact, under certain conditions a car battery may explode while just sitting in a parked car or on a table [source: battery-chargers].
Keeping this mind, here's how to safely use a car battery charger:
- Use the correct charger for your particular car battery. Check the car owner's manual for information (or ask your car dealer or trusted auto mechanic).
- Read the charger manual and make sure you understand how the charger works and what precautions are necessary. Pay close attention to all the warnings.
- Remove both battery cables from the battery terminals. First remove the negative (black) cable and then the positive (red) cable.
- Check that the charger is not plugged in to an electric outlet and that the power switch is off.
- Connect the positive (usually red) charger cable to the positive (+) battery terminal and the negative (usually black) cable to the negative (-) battery terminal.
- Decide whether you want to charge the battery slowly (trickle charge) or quickly. Select a lower charging voltage and current for a trickle charge and a higher setting for a quicker charge. Check the charger manual for the proper settings. Note that trickle charging gives the best results.
- Select whether the charger will run for a specific amount of time or automatically shut off when the battery is charged. Not all chargers have this feature.
- Leave the charger or cables in one place while the battery is charging.
- Turn off and unplug the charger when the battery is fully charged.
- Disconnect the cables, starting with the negative cable, and then moving on to the positive cable [source: CarsDirect].