There isn't much you can do. There can be excessive resistance in the power cables, a problem with the hybrid transaxle assembly, a problem with a convertor or invertor, and problem with the battery ECu, main battery cable, system relay. Who knows.
Sell the Prius and go buy a Chevy Suburban. Who cares what Ed Begley Jr. Thinks. Besides, these cars are sold on the premise that we have to save the planet from Anthropogenic Global Warming.