Perhaps, for vehicles with very short routes. There probably are some places where coal-powered vehicles could be used. For the majority of routes though, I seriously doubt they have the range., given the start/stop nature of postal routes.You might be able to do it with diesel-electrics, which is proven tech, but leftists hate diesel even more than gasoline.
I understand your point but range is calculated at hiway speeds. delivery vehicles will seldom achieve protracted hiway speeds and thus consume less juice as they slowly progress up delivery routes.
There are many classes of postal vehicles. I believe that USPS bought or is buying all new delivery trucks and that is probably what prompted the lawsuit