How do you charge a 12-volt battery in the vehicle?

Per I-CAR curriculum: The following steps are used when charging a partially-discharged battery. With the charger off:

Connect the positive cable to the positive battery terminal. The power switch should be in the OFF position before making connections to avoid creating sparks.
Connect the negative charger cable to the negative battery terminal.
Turn the charger ON. As the battery begins to charge, the analog meter on the charger slowly tapers to zero.
After the battery is charged, turn the charger OFF.
Disconnect the negative cable.
Disconnect the positive cable.

When using a battery jumper or charger, wear proper eye and skin protection. Battery acid is highly corrosive.

Always operate in a well-ventilated area. Batteries generate explosive gases. Avoid making sparks near the battery.

Do not operate with a damaged power cord or plug. Always locate the cord in a safe position.

Do not use with an extension cord unless absolutely necessary, and then only if the extension cord can handle the ampere rating of the charger.

Do not touch the clamps together when the unit is energized.

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