Interesting analysis Jim. A quick calculation of my IV-P's power system energy density (stored useful energy that will come out the prop flange divided by the weight of the engine and the fuel) gives a figure of 0.8 KwHr/Lb.  This compares to the current (npi) technology  of 0.044 KwHr/Lb (battery,+motor+controller) giving a ratio of 18:1. It is therefore true that having batteries with 10X the energy density would make them competitive with hydrocarbons BUT the battery article did not tell the full story. The density improvement was in the silicone ANODE only. The cell now becomes cathode limited and the true improvement in energy density at the cell level is only 2:1. Not shabby, but a long way from 10:1.

Technology marches on and though it may be too soon to be scrapping the old four banger, it's not too soon to dream.

Regards
Brent Regan