hmmmm. interesting question.

May not actually cause a direct reduction of MPG per se, but since the HCH does not have an alternator to power the 12v system, but this is rather recharged by a electronic convertor from the 144v main batteries, two questions arise:

1) Will the additional current drain on the 144v batteries mean that longer "green bar" periods be required, and thus less boost time is available?

2) Will said electronic convertor be able to handle the added load?

I don't know the answer to those questions, but are concerns that I could have.