you have to evaluate the load on the AC generated in KVA and divide by power factor of your load and also of the convertor used by you.
Get KW. multiplying the derived KW by Hours (presuming the the battery is giving same voltage. you get KWH. As this is impracticable to keep battery constant at a known ,
voltage, and the fall of voltage causes increase of load current in DC to ac converters, you have to take an integral value or , i feel weighted average could also approximately help.
Yes, it is complicated.