How to Disconnect the Battery From a Car Alternator

Certain parts of a car, like the alternator, are constantly running electricity even when the car isn't running. Because of this, you must disconnect the battery from the alternator before servicing any electrical components.

Difficulty: Moderately Challenging

Instructions

1. Check the metal ends of the battery cables first. A white powdered substance means they're corroded. Clean them with a wire brush and battery terminal cleaner (or water and baking soda).

2. Check the battery's outside casing for any leaking acid. Wipe up any leaks with a rag or paper towel.

3. Loosen the strap on the negative terminal with a crescent or socket wrench. Two to three turns with the wrench should do it.

4. Remove the connector on the alternator from the negative terminal. The battery is no longer supplying power to the alternator and vice versa.

5. See that the connector is moved as far from the terminal as possible. This will prevent the two from accidentally touching and causing a spark.

6. Disconnect the positive terminal in the same way. Make sure this cable doesn't touch anything metal on the car to avoid sparks.

Tips & Warnings

• It's always a good idea to wear gloves made of rubber or another insulator material. This will protect you from electrical shocks from the battery or from any leaking acid.
• It may not be a good idea to disconnect the battery while the engine is running, especially with a newer model. This can make the voltage rise sharply, damage the engine control module and cause the car to stall.