There are a handful of significantly different hybrid designs. Some of the early designs were in fact just electric drivetrains slapped on to existing gasoline

There are a handful of significantly different hybrid designs. Some of the early designs were in fact just electric drivetrains slapped on to existing gasoline drivetrains, and were more complicated than their gasoline counterparts. But most of the designs that are more popular today are not that. Many of them eliminate some of the most problematic parts on gasoline cars and replace them with solid state components.