They spotweld steel car frames together so I have to wonder what size battery cells the OP is talking about. All of the LARGE cells that I've seen have all been connected by bolted on straps or cables of some sort. The largest battery cells that need to be spotwelded that I'm aware of are D sized cells and a spotwelder can certainly handle those. X-cells are larger but have terminal lugs on them.
The OP needs to tell us more about what she's trying to do.