It is, but it's offset by better efficiency with all other things being equal. The current Prius Prime compared to the Prius is interesting because Toyota trad

It is, but it's offset by better efficiency with all other things being equal. The current Prius Prime compared to the Prius is interesting because Toyota traded performance for fuel efficiency with the plug-in. In the last 2 generations of Prius, Toyota kept performance similar and the fuel efficiency of the plug-ins was better than the hybrids. https://www.fueleconomy.gov/feg/Find.do?action=sbs&id=32484&id=31767&id=37163&id=38531 https://www.fueleconomy.gov/feg/Find.do?action=sbs&id=32484&... At this point, having a larger battery/etc should allow better fuel effective even with more weight assuming the same vehicle, performance, etc...