Here's a random blog that discusses electric Semis: http://www.johnsavesenergy.com/ElectricSemiTrucks.html
He uses 300 miles as a discussion point, which precludes over-the-road use.
There are still a large number of semis that are used for short haul runs, where a 300 mile range would be sufficient.
EDIT: I'm targeting OTR trucks in my comments because that's what self-driving tech most closely targets, and at some point drivers will be replaced. When drivers are replaced, there is no value at all in refueling periods. Currently, drivers use the refueling stop to rest and refuel themselves, but with Self Driving Trucks, you want to be in and out as fast as possible - or perhaps have in-motion refueling similar to aircraft refueling.
I have no background in the topic, but battery tech does seem to be a long-term limitation.
I doubt he'd even combine it with hydrogen, as Nikola says it will, considering how much Musk has been criticizing hydrogen as impractical.