i need help an automatic power inverter

hello room,
i am having a little problem with a project i am building i will like any body with useful information on how i can link a battary charger circuit and a power inverter circuit together to get one a single circuit that can automatically charge the inverter circuit when it is connected to a power supply.And also act as an automatic power back up when there is power failure.Enclosed in this message is the circiuits of a automatic battery charger and a power inverter circuit.
Battery charger circuit

Use a multiple-pole relay.
A relay driver circuit is driven from the mains and when power is present then the load and charger are connected to the mains and the inverter is disconnected from the battery.
When the power fails then the load is changed to the output of the inverter, the battery charger is disconnected and the battery is connected to the inverter.
Power will be interrupted for a moment while the relay contacts move.

If you connect the inverter to the battery and the battery to the charger, you have a UPS (uninterruptable power supply). Why do you want to make it complicated?