Car batteries aren't great for deep cycle use (but can provide rapid heating, most will provide several kW for a short period).
Fortunately they are usually around 35 to 45Ah, which is a big margin.
Say 400A for 40s (assuming battery voltage drops to 8V or so due to internal losses) would give 120kJ and be about 20%
discharge depth or so. Stupidly thick copper wiring would be needed (10mm or so)
A more reasonable 50A for 200s (this time about 12V) would mean more practical heater element and connecting wires (4mm diameter or so)
Alternatively a deep-cycle lead-acid battery at 20A for 8 to 10 minutes... Capacity of 10Ah or more ought to be sufficient for a deep cycle.