Fronius GEN24 PLUS and BYD HVS battery - power in grid down situation?

Looking around online I see Fronius Primo GEN24 with an external transfer switch to switch to battery power when grid goes down. I also see an automatic version but that is is 3 phase.

I always thought, if I had a Fronius primo GEN24 PLUS and a BYD Premium Battery HVS I could power my house when the grid goes down. The sales person I spoke to of a webshop says I need a backup box?

Do I need a backup box?
What is the model nr of this backup box?
What is the switchover time?

My mates have Solplanet with a battery and when the grid goes down, all their outlets continue to work and the lights don’t even flicker. Works amazing but I would prefer a Fornius.

Thank you in advance!