Why does my BMS board get extremely hot when trying to spot weld?

So I have done this before and it worked perfectly on an Iphone XS. But I tried to do it on an Iphone 12 pro max and something really weird happened. I cut off the BMS board from the old battery and I had ordered a new battery with nickel tab on it for spot welding. Everything looks fine and then I wanted to begin spot welding but as soon as I arranged the battery and the bms board in the right direction so I could spot weld my BMS board was super hot in an instant. I quickly seperated it from each other. I couldnt see what I did wrong as I've once done it and nothing happened. So I tried it again. Place the battery and then align the bms board on to the nickel tabs so I could spot weld and again it immediately got super hot. Someone else who has had this issue? Can't understand what I did wrong