One of my co-workers (I'm Australian) has 500 kilowatt-hours of storage at home...which is wild. Much more common is the 10-20 kilowatt-hours of domestic storage for a house.
Fire control in Australia is first and foremost about limiting spread - the bush in Australia goes off if it catches hard.
"Mini" pumped hydro is a thing here (in places): https://www.abc.net.au/news/2024-12-01/australian-first-mini...
If you know your way around high voltage DC, got a tractor and appropriate emulator - not exactly difficult or super expensive to pull off.
Granted it's pretty uncommon setup as grid batteries themselves are pretty cheap too and used EV battery is simply too large for home user, too much hassle, liability, etc to save like $2-3k.
Are they a hoarder of old car batteries and the like?