It's still a decent improvement if they are - one big coal plant running at relatively constant speed is much more efficient than an equivalent number of individual petrol engines in cars afaik.

Coal makes up only a third of American electrical generation, and it’s dropping rapidly.

Coal is one thing, the environmental cost of producing batteries is another. You have to drive your 100kWh Tesla for over 8 years to get carbon emissions lower than ICE cars[1].

That number probably got lower thanks to Gigafactory being more efficient. Hopefully.

1) https://www.autovistagroup.com/news-and-insights/swedish-stu...

Only 30% of USA power comes from coal, and it’s much lower on the west coast than elsewhere.