Even if you don't charge a plug-in hybrid, it will still run on gasoline alone. That's part of the appeal of vehicles like Toyota's astonishingly efficient Prius Plug-In or the more spacious RAV4 Plug-In. Even after it's run out of electricity, the Prius Plug-In is capable of returning up to 52 mpg combined, while the RAV4 Plug-In hybrid is rated for 38 mpg combined running on gasoline alone. That said, the real advantage of plug-in hybrid vehicles is, of course, in using both electricity and gas, but you can't benefit from that if you forget to plug in regularly. Toyota has tried to rectify that via a new app called ChargeMinder, designed to change owners' charging behavior.