I've been doing something similar all along, except for the power off part. My impression is that the Imagio battery is fine, it's the software gauge that is screwed up. Forcing a few recharges seems to make the gauge much more accurate.
I re-flashed about 2 days ago due to a screw up on my part, didn't recharge it that night, and the phone claimed to be at a "critical" (9%) level the next morning. It worked fine all day long and never died. It also never dipped below that reported 9%. In my case, it's definitely the gauge software that's at fault
Good tip regardless. Would be interesting to know if anyone really sees a 2x increase in battery life, and how often these steps need to be taken to make that happen!