Australia

Truck drivers in Australia are banned from driving more than 5.5 hours at a time. There are already dedicated places to stop and park a large truck every 5 hours or so on every single highway.

A truck that can drive five hours on a charge doesn't need that big of a battery. Tesla's semi goes much much further than that on a charge and it would, as you point out, be more efficient if it had a smaller/lighter battery.

I expect where we'll end up is drivers will, when they stop for their mandatory rest, disconnect the trailer, hook the truck up to charging infrastructure, then connect the trailer to a fresh truck with a fully charged battery.

The charging infrastructure would likely be optimised for price, not speed. For example only charge the truck during the day when the grid is running on solar power.

Diesel trucks are not cheap by the way - maintenance plus the cost of the diesel works out to something like a hundred thousand dollars per year assuming you drive the truck all year.

There are too many questions to be answered to calculate how much money you'd save, since electric trucks don't exist at all yet, but my city has started deploying electric busses and they work out to a savings of a quarter million dollars per bus (over the life of the bus). Obviously with savings like that, they are going to stop buying diesel busses entirely as soon as they possibly can. It will be the same for trucks.