When you auto stop, the IMA battery is powering everything thats on. Thats why its level of aggression in regards to auto stopping varies with the IMA battery level. What I've noticed is that I can autostop for MINUTES, and the IMA battery level doesn't seem to go down. This is for one of two reasons that I could think of: A.) one bar of IMA battery is worth maybe 5 to 10 mins of autostop, or b.) the conventional battery eventually helps out, takes over, or some combination of this. And yes, the IMA battery has an integrated starter that is used to start the car. However, I DID leave the lights on one day, and so the IMA battery died, and the conventional battery had to start the car. So it does help the IMA starter if need be. I know because I remember when the car did start after not starting for a minute, the IMA had shown NO bars, nothing. After driving it for a couple of minutes, it charged back up. Can't imagine what would have happened had I killed a few cells in there....