Arguably the highest use of electrical power would be a car at a idling at a long, stoplight in the summer with A/C on, the engine cooling fans on, daytime running lights on, etc.
Since the engine is idling and the exhaust gas flow is low, with the load of the alternator the turbine would probably not even turn.
Which puts all the electrical load on the battery.
Gotta think about sustained worse case scenarios.