I would assume since these are going to be commercial vehicles Tesla will resurrect or otherwise leverage their battery swap idea. Which fizzled out for private vehicles but would really help extend the range of these trucks. http://www.teslarati.com/tesla-to-debut-battery-swapping-sta...

Also more of the tractor can hang underneath the trailer so there's the chance for a larger battery capacity. Like this extended tractor (the semi painted green not the flatbeds behind it) in this image that is 22 feet long. http://www.bigtruckguide.com/wp-content/uploads/2015/01/Sout...