So here are some recent observations I have noted on my car. When the engine is cold and the car is first started with moderate temps outside, if you are gentle - it seems to use the battery over the engine to drive the traction motor.. It will drain the battery down to two bars, after which the engine will start to rev as you are accelerating. After the battery has been drained and the motor is being driven by the engine, the battery will then start to charge. I think that it does this to keep strain off the engine when it is first started up. I also noticed that during this period, as you brake instead of regenerating into the battery, it uses the engine to do the braking as I have heard the engine accelerate when I stopped from a moderate speed. I have been getting VERY good MPG and it seems like it's gotten better overtime (I just hit 50,000 miles yesterday).