There is a fundamental problem with attempting to power an aircraft
with batteries: The propulsion system must not only move the vehicle
forward as it would with an automobile, but it must also
simultaneously maintain the aircraft's altitude;

This is significant at low airspeeds. At higher airspeeds overcoming
wind resistance takes much more power than maintaining altitude.

unlike an automobile
that only requires a small amount of energy to overcome rolling and
wind resistance once in motion, an aircraft can't coast without losing
altitude,

It sure can, until it loses speed and stalls.

Bartek