Until your current car dies, ges old or whatever happens, you decide you need a new one anyway. At that point the ROI is not the total cost of the car but the difference compared to your alternatives.

Yes, the difference. I'm not comparing keeping an ICE to purchasing a new EV. The premium for EVs is $5-10k or more relative to ICE models, and the $5-10k is being very charitable.

Non-peak electricity rate in some parts of California is $0.45/kWh or thereabouts, 2-3x what it is elsewhere in the country.