Electricity isn't just expensive

[nzoomed]

I know people who are using banks of 18650 or 21700 cells in home made battery banks that work well, bit of work assembling them, but if can be cost effective, there is a plentiful supply of the things from e-scooters, etc.
I dont think I would build myself a bank much bigger than 5kWh if I went down that path.
Im definitely doing alot of research on the subject, I have a friend who has also learned a great deal, so any mistakes he made, I will be aware of. There are probably some things I would do different to him already, notably around the batteries used, but he got a one off good deal on the components. He is assembling his battery bank and installing the BMS himself, he is using CATL cells, but I have learned that the EVE cells are actually better and have less issues with them swelling up and the need for clamping properly compared to CATL.
I think I would be best to charge an EV during daylight hours and use off peak hours the rest of the time.

There's plenty of DIY home battery installs on YouTube with many using ex-EV battery packs, particularly from Leafs. Even a ~60%SoH 24kWh Leaf battery has more capacity than a Tesla Powerwall and older Leafs in that sort of SoH can be had for <$6K. If TPTB got V2G cranked up all it would take would be to park up an old Leaf connected to your home's grid and you're good to go with very little effort. The hurdle at present is the price of bidirectional EV chargers and the regulatory hoops involved in doing so.

Yeah there is a ton of information out there on leaf batteries. Ive got a friend thats installing a leaf battery, not just the modules, but the whole battery pack straight out of the car!
Edit: looks like that guy in the link you provided is using the same project on github.
Turns out an open source community has figured out how to hack the leaf BMS and reverse engineer it so they can communicate with the Nissan system meaning no expensive hardware to be installed.
Its pretty awesome what you can do with this sort of stuff, this is where real savings can be made, as you say even with a tired old leaf battery, they still have plenty of capacity remaining for a solar installation.

This guy also has a wealth of information here, no doubt you are probably aware of him.
https://www.youtube.com/@WillProwse