Originally Posted by Beezer
I offered reasons why the battery should be left in & have never heard a good reason why it should be disconnected. I throw this out there when ever I get the chance because I'm still waiting to hear a good explanation. I contend that the battery might save a system from damage rather than make it more vulnerable.
as for the long way 'round guys.... the welder melted some wires
I would not be too worried about leaving a battery connected during welding, I think the main thing is keeping the ground connection very near where you are welding and keeping the two wires from the welder close to another to reduce the loop area.
However, I think there is some logic to disconnecting a battery. This is just based on thinking about the problem, I have never done any measurements to determine how true this is in the real world. When you are welding you are causing large transient currents which will cause large transient magnetic fields. If there is a wire loop from the battery to some electronics and back to the battery this changing magnetic field will cause a current in this loop which could cause a higher voltage than normal across the electronics. The low impedance of the battery will not prevent this voltage from being generated.