Wouldn't it make sense for fleet vehicles, like buses, to be designed with interchangeable power/battery packs? The batteries can be charged when electricity is cheapest, and, during the day, the vehicles can change battery packs without having to wait for the drained batteries to be charged.

Oregon does not have a sales tax and most likely will not have one any time soon. If you do not have a brick-and-mortar store front then register your company in Oregon. Some states may still require a sales tax but the responsibility falls entirely on the consumer to report it and pay.