In each self repair book you can read: "Disconnect the battery first before welding!"
Well, I had to welder only at the rear of my cars so far, and because I couldn't find any plausible explanation why to disconnect the battery, which is in the front near the motor, when welding at the rear, I never disconnected the battery before welding and never had any troubles. I had the ground tip of welding machine always in closest distance to the repairing location, though. So, where else should the current flow than through the small loop of the repairing location??

Do you know, why the battery shall be disconnected while welding, dear Steve?

Kai