Or make the trailer itself have a large battery in it that the truck just hooks into, then the truck only needs a small capacity battery to handle moving from trailer to trailer. Then the trailers can charge while they are empty or during loading/unloading.

Trailers are vastly cheaper than the truck. I think it is insolveable to depend on battery loaded trailers. You lose so much flexibility with such a setup. Much better to keep the battery in the truck.

yeah, you are probably right. I guess in the future if you don't need a cab (no human driver), and you don't need heavy fuel tanks (plus full fuel weight), you can use much of that space to put quite a bit of battery.

How does that work if you own the truck?

If you own the truck you can charge it at night when you're not driving it. The kind of operation described above seems to imply fungibility of trucks.

isn't the idea that trucks will be self-driven? in that case one company will own multiple trucks. in the meantime, if you are independent driver who own's the truck, you could be switching trailers with different cargos. you deliver the trailer to some point, unplug it, recharge, plug in different trailer and continue to its destination.

or are you asking me if I own a track and how the mechanics of truck/trailer works?

no i don't own the track and this https://upload.wikimedia.org/wikipedia/commons/thumb/3/3e/Co...