I am thankful for the simple shields I can put on my car early on, but because they have idle power drain, over time they chew through any fuel I put in the generator as the car sets idle. If I park the car at some sort of top-off station, I can fuel the car itself, I can plug the car's inventory chock full o' coal, but none of it goes into the generator.
Am I missing something? Is there any way to make this happen? If I want to put generators (or, later, the fusion/antimatter gens) into trains to make some sort of automated repair train that can run around, am I going to have to manually refuel those? Is there any way to know they need refueling?

Yes, it would be very convenient, but unfortunately the game doesn't provide for such a possibility. All I can do is increase the fuel capacity from one cell to two or three. Also I can add a new level of solar panels that would be more efficient.

I haven't gotten to solar panels yet, so I can't speak to balance. For automatic trains, I'm sure they'll be fine though, with batteries.
Was mostly wondering if I could get something going in the early game until I get panels going, without having to micromanage it. The shields don't loose hitpoints when out of power though, so it's mostly just a minor inconvenience for my car.