As a point of view, you don't need (and probably shouldn't buy) a battery that satisfies your peak usage. That would be a waste and would be over buying. Instead, a smaller battery that meets your energy needs on 80% of days is probably a better investment. However, only charging your cars at night probably saves a good part of your energy costs. If you're interested, here is a YouTube channel that talks about energy usage with solar panels, heat pump, EV, and batteries.

https://www.youtube.com/watch?v=4zDRDFSUxbI