what is a prius eco?
<answer> The Toyota Prius Eco is a base model of Prius fitted with a lithium-ion battery pack. <context> The 2016 Toyota Prius actually has two separate versions, when it comes to gas-mileage ratings. Most Prius models this year are rated at 52 mpg combined (54 mpg city, 50 mpg highway). But the 2016 Toyota Prius Eco, which is essentially a base model fitted with a lithium-ion battery pack that's smaller and lighter than the old-school nickel-metal-hydride pack in the entry-level Prius Two model, does better than that.