[Mr. Pancake]

MetroMPG you've got it exactly right. The best way to efficiently use Honda's IMA system is to not use it (for acceleration, at least). I use a switch to disable assist at least 90% of the time. I do allow regenerative braking when I need to slow down and I prefer auto-stop to turning the car off. I also like the quiet engine start using the motor rather than the starter.

You probably would still get better mileage with a healthy hybrid battery. Your 12v battery would be charged from the hybrid battery instead of the electric motor like it is now which is causing some additional load on the engine and may be causing it to be a little harder to get and/or stay in lean burn. I'm also unsure of the service life of the insight's starter, my car used its starter twice last year. Both times the temperature was below zero (farenheit).