How much watts of current an inverter takes to charge its battery to run an electric appliance.?

How much current an inverter consumes to charge the battery to run a 100W home appliance for one hour. I would like to know is it economical to use inverters instead of electricity supplied by government, at peak times. To be precise, if an inverter works for 500 w equipments conteneously for 8 hours, the total output is 4 KW, whether the current required to charge the battery will be 4kw or more?