I did want to come back to cost for a bit.
Average US cost for gasoline in 2007 in terms of KWH ~
$0.25/kWh (I know, I know)
Average US cost for electricity in 2007
$0.09/kWh
People may not understand WTW and mpge, but everyone understands cost.
Yes, have standard conversion built in and applied to the whole garage. Diesels should probably have a correction factor too by that logic.