the battery packs can propel the car for hundreds of miles on a single charge. teslas even come with a camp mode that can run the hvac if you wish to stay in the car for an extended period of time like overnight. hvac has very little effect on a battery pack that is made to power motors at highway speeds for hundreds of miles a charge.
your understanding is more confusion of what you're seeing. what you think is a 'diesel generator' is actually a large power inverter. It flips the electricity from AC to DC.... it's the same concept of like how you have a power brick for a laptop computer.
i've been studying a lot about simulations and 'aliens'... the most calming part of it all to me is the chaos. things would be boring as heck if we didn't have these topics and ideas to explore.