Yes, the green level goes down indicating the State of Charge (SoC) of the HV battery. If it's not going down, you are not driving in electric only very far. As the level gets near the bottom, the engine will "start" to recharge the battery. You don't need to fill the battery till you can go EV again, just put a little more juice in it automatically with the small generator or use the Fake Shift in "L" for heavy regen charging with the traction motor/generator.

GaryG