Is this in an imaginary world with no power from anywhere else, including international interchange? Total battery power is a society ending event. It’s hard to speculate on a power situation that doesn’t exist.

Costs are based on supply and demand. At current demand battery power back up is cheaper than non environmentally friendly forms of energy. Should that change due to supply issues, we can recalibrate.

Howevwrx the smart money, which happens to also benefit the environment, is on green energy.