Frequently asked questions about disconnecting a car battery safely at home. Answers below apply to most passenger vehicles with a standard 12-volt lead-acid battery in the engine bay.
Official answer: disconnect the positive (+) battery terminal first, then the negative (-) terminal. Never remove the negative clamp before the positive clamp.
Removing the positive clamp first isolates the main power feed before you loosen the ground strap. Keep the loose positive clamp away from grounded metal while it is off the post.
Wear gloves and eye protection before you work near a car battery. Park on level ground, engage the parking brake, and switch off the ignition. Work in a ventilated area away from open flames.
Identify the battery polarity before touching cables. The positive post is usually marked with a plus sign and often has a red cable or boot. The negative post connects to the vehicle chassis ground.
Remove the hold-down bracket or strap that secures the battery in the tray. Lift out the old car battery using both hands and keep it upright.
Clean corrosion from the battery tray with a wire brush and baking soda solution. Dry the area before setting the replacement battery in place.
Set the new car battery in the tray with terminals oriented to match the cable reach. Secure the hold-down bracket snugly.
When reconnecting, attach the positive terminal first, then the negative terminal. That is the reverse of the removal order.
Start the engine to confirm the charging system is working. Voltage at idle should rise into the 13.5 to 14.5 volt range on a healthy alternator.
Reset clocks and radio presets that lost power while the car battery was disconnected.