REVIEW: 2017 Audi Q7 e-tron TDI Plug-In Hybrid: It’s a diesel-electric plug-in, like a locomotive with a cord. “The e-tron TDI can’t match the dynamic excitement or Bentley-baiting torque output of the SQ7, but it’s fast, well-mannered, and—so long as it’s plugged in often enough—capable of turning in exceptional fuel-economy numbers. Then there’s the prospect of being able to go more than 800 miles between fuel stops to replenish its 19.8-gallon tank, provided you drive gently enough.”