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

[McLucia]

Turn off the vehicle engine and remove the key. Disconnect the negative terminal cable from the battery first. Then disconnect the positive terminal cable. Remove the battery protective cover, unscrew the battery fastening bolts, and take out the battery for replacement. The main reason for disconnecting the negative terminal first is that the negative terminal serves as the ground connection. Once it's disconnected, any accidental contact won't cause issues. However, if the positive terminal is disconnected first, theoretically there's no problem, but there's a risk: improper operation may cause the wrench to touch metal parts of the car body, potentially creating sparks. This essentially creates a short circuit between positive and negative terminals, generating a massive instantaneous current. In severe cases, it can blow the vehicle's main power fuse, with the most common consequence being damage to the car navigation system. There's no problem if the disconnection sequence is reversed, but for installation, connect the positive terminal first followed by the negative. For removal, disconnect the negative first then the positive. This distinction in operation sequence is specifically to avoid accidental grounding of the positive terminal during battery replacement. For vehicles equipped with keyless start systems or those with numerous high-tech configurations, never disconnect power when replacing the battery - never disconnect power, never disconnect power. The most common issues after power interruption in such vehicles include unstable idle speed requiring recalibration; various fault codes appearing on the dashboard needing reset; engine stalling immediately after starting, and other malfunctions caused by battery replacement. Sometimes these faults can't even be resolved through recalibration, so it's best to avoid power interruption whenever possible.