When a car is not driven for a long time, should the positive or negative terminal of the battery be disconnected first?
2 Answers
When a car is not driven for a long time, the negative terminal of the battery should be disconnected first. The negative terminal of a car is connected to the car body, which is made of metal. The entire car body is connected to the negative terminal, meaning the car body itself acts as the negative terminal. This allows the negative terminals of any electrical components to be connected to the car body for grounding. The current will return to the negative terminal through the car body, eliminating the need to run a separate wire from each component to the negative terminal, which significantly reduces the amount of wiring and makes circuit troubleshooting easier. If the positive terminal is disconnected first, since the wrench is metal and conductive, it may accidentally touch a metal part of the car body during the disconnection process. This would directly connect the positive terminal of the battery to the negative terminal, causing a short circuit.
As a veteran driver with over 20 years of experience, I always disconnect the negative terminal first when leaving my car parked for extended periods. Why? Removing the negative terminal is safer because the vehicle's body frame and engine components are typically connected to the negative terminal, acting like a large grounded metal shell. If you disconnect the positive terminal first and accidentally touch any metal part of the car body with your wrench while working, it creates a direct short circuit between the positive and negative terminals—resulting in instant sparks or even damaging the electrical system, which is no trivial matter. Prioritizing the negative terminal avoids this risk and also prevents battery self-discharge (e.g., electronic systems slowly draining power in standby mode). Before disconnecting, ensure the engine is off, use an insulated wrench to loosen the bolt, and wrap the disconnected terminal with electrical tape to prevent oxidation. Additionally, park on level ground and maintain proper tire pressure to avoid deformation. Batteries also degrade over time when unused—if possible, recharge every 1-2 months or use a maintenance device to extend their lifespan.
