https://www.youtube.com/watch?v=an6e2Lh9u58Ok sorry about the title it's just what popped to mind (yeah I know I am a bit of high/low tech weird).
We know that our buses really need a very large battery pack if they are going to be fully electric.
However the following YouTube video describes a extreme heavy truck application where they get by with a 250KW battery pack where a daily requirement would be three megawatts, by replacing the prime mover engine with a generator/battery hybrid combination and save 50% on fuel...
They are talking two to three hours of operation before even firing up the generator, so I would envision driving four to five hours with battery and a smaller generator.
Enjoy and hey comment!!!