I should qualify why: The South Australian power network, due to its increasing reliance on Wind and Solar, struggles with fluctuations in the network. The battery will aid to stabilise the grid in peak demand times.
This paper, in which the authors develop an argument that market structure and incentives for frequency control are driving instability, is worth a read:
The really big 2016 blackout in SA also wasn't caused by wind or solar energy, but that doesn't mean that stabilising the network isn't something that won't be required if the energy production develops more towards renewables.