Micheal, think about it like this; Under normal cruising, driving any automobile does not require much power. IIRC, the typical car on the highway only requires ~40hp. So why do we not just put 50hp engines in every car? The answer is that to accelerate it requires much more energy than it does to cruise. A normal automobile must have an engine sized to meet every energy requirement, even though it rarely needs it. An ICE is, in a sense, a 'jack of all trades, master of none'. Using a small ICE to drive a generator, offers two benefits. First, it allows you to operate it at the level in which it produces its highest efficiency (BSFE?). Secondly it allows you to use a much smaller engine. The engine does not have to be sized to meet pathological conditions. It can be sized to a level that under normal circumstances it would produce a small surplus of energy that can be stored in batteries. Typically the small ICE would be able to offer just enough power to cruise while generating a small surplus that will be stored in the batteries. Under conditions in which you need more power than is currently generated, the propulsion system will be able to draw upon the energy stored in the batteries.
