[MetroMPG]

FYI, a functioning hybrid battery isn't strictly necessary to get fantastic fuel economy from a 1st gen Insight.

I mostly drove my Insight with assist/regen switched off. It still blew away the EPA ratings. But I also used many techniques to do so, and almost always took the scenic route when on highway trips (~50 mph).

Provided the 12v battery continues to be charged (it seems some do and some don't when the pack is shut off), the car will be more sluggish but acceptable without hybrid assist (if you consider slightly better than Geo Metro levels of power acceptable).