You don't need power for the whole trip. If most of it can be electrified with wire and you only have small patches which cannot (like the tunnel mentioned) cur

You don't need power for the whole trip. If most of it can be electrified with wire and you only have small patches which cannot (like the tunnel mentioned) current battery technology is up to the task. We will introduce that here in the near future for a new tram line going through a park (where we don't want overhead wires).