Should we get more home battery capacity?

[Everest]

That sounds like a great idea, but there is no reason why you couldn't also plug in the 48 V DC battery charger to the same circuit and top up the house battery from the EV's V2L output when there is no mains power, so the devices powered from the battery can be kept powered up as well.

I agree, but there could be a caveat in that as Rolfe's installer said it is not possible it could be that Rolfe's system uses HV batteries, rather than standard 15S or 16S "nominal 48V" low voltage system. As far as I can see, Givenergy have both LV and HV systems