would a good solution not be to have electric busses with batteries, which also have the umbilicle on a spring loaded or electronically actuated system to raise it to connect to the wires?

Trains. Believe it or not. Boston still uses deisel commuter trains, including one “deisel under the wire” on the electrified Amtrak line. Everyone has been pushing to electrify but it’s expensive. Their solution is battery trains. They can run them on battery now, while tAking power from catenary as it’s built. Seems like a huge waste of money, but I guess you have to transition somehow