I get the 'angry bees' at low speeds after battery depletion, but no noticeable loss of power. And, while there is still charge on the battery, I have never noticed any change in the way the car acts. If the battery runs out at highway speeds, it's very hard to notice the change to ICE. Even when I'm listening for it, it's pretty hard to hear over highway noise, which is totally dependent on the type of road. Even on quiet smooth pavement the ICE is not loud at speed.