The CSIRO renewables plan factors in only 2-4 hours of battery capacity (way less, with some already built) with the rest of the backup coming from existing pumped hydro and an existing Natural Gas plant. one of the reasons nuclear looked worse in the report is that they would have to actually build a nuclear power plant. it might not make direct sense to build nuclear given what already physically exists, but apples to apples it's not quite as clear.