> Why would it be different from swapping out a propane tank in my gas grill?
Because we are not talking about propane. We are talking about a tank storing highly pressurized hydrogen, which is way more difficult to handle than propane. In a moving vehicle, not a grill.
> Lithium is expensive to mine
Yes. It can be mined once and then reuse countless times, however. Hydrogen is expensive to manufacture too, and it's "burned" so you always need more.
Expect prices to go down as more infrastructure to mine and refine is put into place. This is even ignoring technological advancements in extraction - which tend to happen once there's demand.
> electricity is usually produced by burning coal
This is highly location-dependent. True for some places, not true at all for others. That's also becoming less true by the day.
_Even_ in the case where 100% of the grid power worldwide came from coal, EVs would still be a win. The generator on a huge power plant is far more efficient than any car engine. And the pollution is concentrated on a few places - places we can improve. Additionally, there are no emissions on population centers, meaning an enormous improvement on quality of life and a decrease on deaths due to respiratory illnesses.
Then, once you upgrade the power plants, the entire vehicle fleet gets an instant upgrade.
If it's in your means (essentially, if you own your property) you can generate power from renewables on site and power your vehicle that way. Try doing that with hydrogen.
> and can our current grid even handle 100% electric vehicles
Yes according to the US Department of Energy.
> I mean it's better than gas, but it's not the end of the road of vehicle power is it
Just until we find something better, then we'll _easily_ change our vehicles to store electric energy using the new storage device. That's the good thing about electric motors, they don't care where the power comes from.