Amps times volts is power used. 1.2 Megawatts at 12 Volts is 100,000 Amps! Your typical wires would not melt , they would vaporize! It would end your battery charge real quick!
It’s not quite that bad but your point is still valid. The battery pack is probably somewhere between 500 and 800 vdc rated taking the best case scenario of 800 volts it would require a 1500 Amp connection. That is usually a bus bar not Cable.