Two functions in one makes our inverter more adaptable.
The inverter itself can convert DC input into AC output, with the pure sine wave form.
And the built-in charger can also fulfill charging function to charge batteries.
So you can imagine the scenary where the wall outlets power the battery via our inverter, and the inverter also connects to the appliances. And the result is that the appliances are powered by the mains electricity when the electrical network works well.
When the electricity cuts off, the inverter will power the appliances with supply from batteries.