Medyo mali yung question since power station just store a power, kung kakargahan mo ito gamit yung power outlet mo, technically you're just charging a powerbank at nabibill ka pa din sa same price ng electric company.
If gusto mo makatipid, you need to pair that power station with a Solar Panel, ikaw mismo mag generate ng electricity without the help of the grid (off grid), lahat naman ng power station is may solar charging input na.