> Transforming cells, via modules, into the whole battery pack typically adds 30% cost per kWh on top of the cost of the cells alone.
And to get a bit more info on what a module is [2]:
> A battery module is more than just a mechanical frame that holds the cells - it also includes bus bars to connect the cells electrically, a cooling interface and a sensing harness, which sends information about the state of each cell to the battery management system.