Battery storage doesn't need to be cheaper than nuclear on a kWh vs kWh basis, because you only need about 5 hours storage to get to 98% renewables.

The combination of solar and wind and battery storage needs to be cheaper, and it is. The CSIRO, who factored in all costs on both sides, found that it's about 50% of the price of new nuclear in Australia. This conclusion may vary in places with less sun or an existing nuclear industry with a track record of building cheap plants quickly.

Note also that a nuclear grid will also need battery storage because demand itself is variable. Unless you overbuild nuclear and run at a low capacity factor, but that carries with it its own additional costs.