It’s DC current. Only a change in current flow broadcasts anything.
I am not saying if this is all B.S. or not because I don’t know. But Just because a battery is DC does not mean anything. There are large pulsating currents abound in an electric car. Current to the motors is constantly changing and they do draw a lot of it. Whats more I assume that motors are supplied current by way of a PWM drive. That would mean they are fed a square wave at a certain frequency. Therefore all of the wires feeding those motors are going to emit a magnetic pulse. I am not certain if the changing currents from the batteries themselves would cause the battery to also emit a pulse. The battery does contain conductors. The current is changing a lot. So it is possible, but I would think that the real EMP’s would come from the external wires themselves.