I cannot see a spec for that machine online. Most ordinary automatic washing machines that have a water heating element built in use in excess of 2000W when heating, I assume yours is designed to fill with hot water and does not heat it? I also wonder about the motor power quoted: if dehydrating means spinning that would typically be a higher load than washing.
I agree with Marvo about the electronics. To explain his point further, many washing machines that do not have a direct-drive permanent-magnet motor use a universal brush-motor with phase-angle speed control. These WILL NOT work with 'modified sine' and the speed controller may be damaged. Older machines used induction motors which will generally work but the motor power may be reduced and the load on the inverter greater than would be expected.
Finally, even at 450W, with an inverter efficiency of 90% the load on a 12V battery would be around 42A which will require a decent size battery if it is to run for long.
