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Should the positive or negative terminal be disconnected first when disconnecting a car battery?

2 Answers

Bentley

07/24/25 5:52am

When disconnecting a car battery, first disconnect the negative terminal, then the positive terminal. When reinstalling, connect the positive terminal first, followed by the negative terminal. Disconnecting the battery cuts off the power supply to the starter, preventing the engine from starting and the vehicle from operating normally. After the battery is disconnected, when the car is stopped and the alternator ceases to function, the entire vehicle loses power. Consequently, the vehicle's anti-theft system will not operate, and neither the alarm nor the lights will function. Below are some tips for car battery maintenance: 1. Avoid prolonged parking: The battery installed in the car will self-discharge over time when left unused. It is advisable to drive the car at least once a week for a minimum of 20 minutes to allow the battery to recharge while driving. 2. Close windows before turning off the engine: The power for operating the car's windows and sunroof comes from the battery. Therefore, it is best to close all windows before turning off the engine, rather than after, or using the long-press lock button method to close the windows after leaving the car. 3. Keep the battery clean and tidy: Regular inspections are an effective way to extend the battery's lifespan. Use a professional battery terminal brush or an old toothbrush to clean dust and corrosion from the battery's positive and negative terminals. Applying petroleum jelly or a greasy substance to the contact surfaces can create a protective layer.

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LeHolden

08/11/25 1:34am

I remember one time when I was repairing my car and wanted to disconnect the battery to replace a part. I accidentally touched the positive terminal, causing sparks to fly everywhere and nearly damaging the electronic system. Since then, I always disconnect the negative terminal first—the black cable marked with a minus sign. The negative terminal is connected to the car's chassis, and disconnecting it breaks the circuit, reducing the risk of a short circuit, making it safer. If you disconnect the positive red cable directly, it’s easy to accidentally touch metal parts, causing sparks or worse. The correct steps are simple: use a wrench to loosen the negative nut, then remove the positive terminal if needed. Regularly check the battery terminals to ensure they’re clean and free of corrosion, which can extend their lifespan. This habit has saved me a lot of trouble, especially during DIY repairs. Always remember to wear insulated gloves just in case. Car safety comes first—paying attention to small details helps protect both yourself and your vehicle.

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