Unchanged for 2019, Buick’s full-size sedan is now the only model of its type in the brand’s lineup since the Regal became a hatchback. For 2018, a four-cylinder “light hybrid” engine assisted by a motor-generator and attendant lithium-ion battery pack became the LaCrosse’s base engine. It produces a combined output of 194 horsepower and 189 pound-feet of torque. The result, according to Buick, is a nearly 20 percent improvement in city fuel economy, compared to the optional V-6. The so-called eAssist also kicks in when accelerating from a dead stop. The accompanying battery pack that’s stored beneath the rear bench is compact enough so that the seatback can be lowered for increased stowage space. The system’s regenerative brakes also help replenish the batteries by converting kinetic braking energy into electrical energy when braking or coasting without using the throttle. A six-speed automatic connects to the I-4, while a nine-speed unit is matched with the V-6. That engine is mandatory if you wish to add all-wheel-drive to your LaCrosse.