I have no idea where you got these numbers, but nuclear energy is good for base load, while batteries are good for handling load peaks. These two types of load are very different.

With big batteries, nuclear energy can be accumulated at night and used at evening, which improve performance of nuclear stations a lot. Try it yourself at simulation: https://www.tennet.eu/fileadmin/user_upload/Our_Key_Tasks/In...

Current cost of power storage is below $100 per kWh stored in the newest designs.