The article doesn't say how they got that levellized cost figure. How much do they think 17kWh of battery costs?

From my research, a home battery costs, per kWh, about 8x an electric car battery and I don't know why.

Last month in China BESS auction went for around $56/kwh that's not just the battery but the whole system. So the numbers they used are probably more than current battery prices.