not really im a welder by trade and the underneath of the car can act like a farady cage and store electricty any ac current can effect circiut battery or not
No it can't. A Faraday cage is conductor, and dosen't store anything. To do any damage you need a circuit. Disconnecting the battery, break's the circuit. Welding of steel in done using DC, only TIG welding aluminium is done using AC.