Behind the Wheel | 2014 Honda Accord Plug-In and 2013 Ford Fusion Energi: Aiming for the Hybrid’s Sweet Spot

What, then, should we make of Ford Fusions and Honda Accords suddenly sprouting plugs and growing battery packs? Both of these mainstream, top-selling cars have recently arrived as plug-in hybrids, expanding their maker’s existing lines of gas-only models and conventional hybrids.

You can think of a plug-in as an overachieving hybrid, a vehicle that runs largely on electrons for local miles and then mostly on gasoline for longer trips. That combination — a broadly appealing solution that splits the difference between petroleum power and purely electric cars — has the potential to make battery propulsion acceptable to motorists put off by matters like limited driving range.

The Ford Fusion Energi, however, is less about the blending of electrons and hydrocarbons for power and more about the car’s dual nature: the ability of a handsome family sedan to switch, superhero-style, from one driving persona to another.

When its 7.6 kilowatt-hour battery pack is fully charged — that takes about 2.5 hours from a 240-volt source — the driver can invoke the car’s jazzy smooth electric-vehicle self. In the first two days of a week with the sedan, I used a button near the gearshift to select the EV Now mode, which keeps the car driving almost exclusively on its battery. In 36 miles of driving punctuated by frequent electric top-ups, I was effectively operating a spacious 3,913-pound zero-emissions electric sedan, not using a drop of gasoline.

The car’s roomy interior, comfortable ride and taut steering were a welcome change from the toylike robotic feel of the Nissan Leaf compact E.V. that is my usual transportation. Among sedans that can operate on battery power, in my view, the Fusion Energi is surpassed in size and style only by the Tesla Model S.

Both cars appropriated Aston Martin’s signature grille to inject some James Bond flair in their four-door profiles. But don’t take the similarity too far: compared with the rip-roaring Model S, the Fusion Energi has swallowed a dose of Xanax. It glides sedately through city streets. The acceleration on highway on-ramps is adequate, but when driving solely on electricity, the car is not even as zippy as a Leaf.

Things change about 17 or 18 miles down the road, when Dr. Electric transforms into Mr. Combustion. With gasoline supplying power via Ford’s 2-liter 4-cylinder engine, and assisted by the electric motor and battery pack that had been operating solo in E.V. mode, the car’s output jumps to 188 horsepower. It feels like twice the oomph.

Ford has perfected smooth transitions between gas and electric power sources, so passengers have little evidence of the handoff. The cabin of the Ford Fusion Energi is also among the quietest I have experienced. Close the door and you feel practically vacuum-sealed, buffered from engine noise or vibration. Noise-cancellation technology is used to counteract any whine from electrical components.

After the switch from E.V. to hybrid operation, there is an obvious sign that hydrocarbons are powering the Fusion: the planted feel on the road now takes on a sporty quality. It becomes a fun family cruiser, especially shining on the highway, territory not usually associated with E.V. prowess.

An 80-mile round-trip drive between Berkeley to San Jose — usually an anxious experience in my Leaf requiring a 55 m.p.h. pace to conserve energy — was carefree in the Fusion Energi, which offers a total range of 620 miles.

Yet the Transformer-like shift has an impact on efficiency. There were several days early in the week when I frequently charged throughout the day, and therefore remained all E.V. As a result, fuel economy broke past 100 miles per gallon of gas (not including the electricity you put in the battery). The E.P.A. pegs average combined city-highway fuel at 100 m.p.g.e. A Toyota Prius plug-in, for reference, is rated at 95 m.p.g.e.

Trips that started all-electric for the first 20 miles or so but continued on for another 50 or miles registered around 75 m.p.g. And the day’s travel to San Jose and back — when I tested the limits of legal highway speeds, with air-conditioning and audio blasting — fuel economy was a respectable 38 miles per gallon. Over the course of 227 miles, the Fusion Energi averaged 55 m.p.g.