The charging the battery from the grid on its own is interesting in spaces where the TOU between 4-7pm (or whatever yours is locally).

Here it is more than 3x, so if I can charge a battery and run off of that for those 3 hours, I am saving money.

And it's not that I can lose money, a charge in the battery doesn't become stale.

Don't forget to account for the additional battery wear from extra charging and discharging. However your cost saving probably exceeds the wear cost.