DIY Capacitive Discharge Battery Spot Welder
They have around 0.030 Ohm of internal resistance and at 2.7V the maximum current they can output will be I=2.7V/0.030Ohms around 90 Amps that is low for a Spot welder. If you place the capacitors in parallel, for example two, the maximum current will be around 180A, but the voltage will be low (2.7V).