A battery pack in an EV consists of a large number of individual battery cells that are held together mechanically and connected electrically. Making those mechanical and electrical connections poses several challenges, including the joining of multiple thin, highly conductive materials of varying thicknesses and potential. The key aim for the electrical connections is to produce a joint with a low electrical resistance to reduce the energy loss through resistance. A battery pack has to use different materials, and this creates a challenge for joining dissimilar materials. It can create brittle intermetallic layers with higher electrical resistance and a. Resistance spot-welding (RSW) exploits the electrical resistance at the mating surfaces when high current passes through them to create localised heating and fusion of materials. Nevertheless, ultrasonic metal welding is one of the most commonly used methods. It has been used for various electric cars, including the Nissan Leaf.