Why mess with success? The Q5 is best-selling model in the US by a long shot. Adding a plug-in hybrid powertrain could've given Audi the opportunity to throw even more changes into the mix. Instead, the automaker stayed on its heading and left the rest of the vehicle alone. The result is predictable, but the good kind of predictable.The has never been the most striking vehicle on the road, preferring a demure appearance that's more about fitting in comfortably. Some automakers, like Audi's kissin' cousin Porsche, draw attention to their plug-in with a dash of aesthetic conspicuousness by way of hybrid badges, brightly colored brake calipers and the like. But not here -- the PHEV looks barely any different from a gas-powered Q5, save for the second gas flap that hides the charging port and the larger brakes borrowed from the to balance out the heft of the battery. My Premium Plus tester looks especially vibrant with its $595 Ultra Blue Metallic paint job, and it has a little extra street presence by way of upgraded 20-inch alloy wheels, an $800 option.Slip inside, and it's immediately apparent that Audi nailed the fit-and-finish game. The Q5 PHEV's interior is absolutely befitting of its hair-over-$50,000 starting price, with a mix of materials that are nice to both observe and feel. My tester's no-charge birch wood inlays are lovely, adding a small pop in an interior that's otherwise conservative. From a livability standpoint, the Q5 gets full marks. This Premium Plus tester adds $3,900 over the base trim, but it includes niceties like autodimming side mirrors, keyless entry, a wireless device charger, a panoramic sunroof and a host of safety-suite upgrades. The Qi charging pad might be my favorite part, because it's capable of sliding out from underneath the center armrest for easy access, otherwise staying stowed out of sight for safety's sake. That leaves plenty of room ahead of the shifter for tchotchke storage, although the sizable door-card cubbies do a great job as stash spots, too.The rear seat is a little on the tight side, but at 6 feet tall, I'd be comfortable enough to tackle longer trips. Storage options are a little lighter, as well, with some cargo nets on the front seatbacks and smaller door-panel pockets, but hey, at least there are two USB ports back there. Moving farther back, I'm glad Audi was able to fit a PHEV powertrain in the Q5 without sacrificing cargo space, which remains a solid 25.6 cubic feet. Sure, there's a bag with all the charging equipment back there, but you can leave that in the garage if you only ever plug in at home or at public chargers. Under the Q5 PHEV's hood is the same 2.0-liter turbocharged inline-four that powers the base Q5, making 248 horsepower on its own. This combines with a 141-hp electric motor and a 14.1-kilowatt-hour battery pack to produce a net 362 hp and 369 pound-feet of torque, all of which is routed through a seven-speed automatic transmission to all four wheels. It's markedly quicker than the base Q5, arriving at 60 mph in 5 seconds flat instead of 5.7, but it's also carrying around an extra 540 pounds. Acceleration is sufficiently zippy in around-town use, especially when it's operating in EV mode, with all that delightful, immediate electric torque.The 14.1-kWh battery offers an EPA-estimated range of 19 miles, a number I found pretty easy to match in real-world suburban driving. The highway absolutely chews through the battery, so I find myself tapping the EV button on the dashboard to maintain the pack's charge at higher speeds. Driving around in electric mode is great; the cabin is nice and quiet, and the federally mandated low-speed EV noises are futuristic but not annoyingly so. When it comes time to charge, a Level 2 charger will top 'er off in about 2.5 hours, with a standard three-prong 110-volt plug extending that charging time to an overnighter.If the battery reaches a near-zero charge, that's when the Q5 PHEV operates like a traditional gas-electric hybrid, using small doses of electric operation to boost the car's overall efficiency. However, this is where my one issue with the car appears: Applying light to medium throttle from a stop will have the car start its journey with electric power, only to stutter when the gas engine fires up as the transmission shifts into second gear. If you're especially uptight about keeping the battery charged, this problem will never make itself apparent, otherwise some adjustment in the footwork department will keep this issue from cropping up. Otherwise, the Q5 PHEV's driving experience is absolutely lovely, just as it is with the base model. The suspension does a good job of eliminating nasty roads underfoot, even with my tester's larger alloy wheels. The brakes do have a bit more bite than the base variant, but pedal modulation is dead simple, and the blend between regenerative and friction braking is nearly impossible to suss out.Overall, the EPA rates the 2021 Audi Q5 PHEV at 50 mpge, which is a bit lower than what you'll find from competitors like the BMW X3 xDrive30e (60 mpge) and the Mercedes-Benz GLC350e (68 mpge). That said, PHEV efficiency varies wildly in real-world situations, depending on how often the battery is charged and how long trips take. In my week with the Q5, I find the Audi's EPA estimates to be easily reachable with regular access to a plug or a public charger. One final word of warning here: The Q5 PHEV's gas tank had to shrink to accommodate the hybrid bits, condensing from 18.5 gallons to 14.3 gallons.The Q5's tech goes beyond what's under the body panels. A new 10.1-inch screen sits in the middle of the dashboard, running the latest iteration of Audi's MMI Touch infotainment suite. I love this system's straightforward menus and graphics, and it's always pretty responsive. Android Auto and Apple CarPlay are standard, with the latter boasting wireless capabilities, but if you want an in-house option, embedded navigation is a $1,500 upcharge on the Premium Plus trim. My tester also comes with Audi's 12.3-inch Virtual Cockpit Plus, which puts just about everything from the main screen closer to my eyes, and it's easy to wade through its various modes with steering wheel buttons and thumb wheels. Audi has always been good at offering a complement of standard safety technologies, and the story is the same with the Q5 PHEV. Standard kit includes automatic emergency braking, forward-collision warning, lane-departure warning, parking sensors and automatic high beams. The Premium Plus trim adds adaptive cruise control, active lane-keep assist and a surround-view camera system, all of which are easy to use and make daily commutes a less frustrating affair.While a base 2021 Audi Q5 will set you back $44,395 (including $1,095 in destination charges), the PHEV is a little pricier, starting at $52,995 before any EV-related federal or local incentives. My tester takes that window sticker a little higher; the Premium Plus trim, in addition to options like fancier paint, navigation, a Bang & Olufsen sound system and bigger wheels, brings my tester's out-the-door price to $60,740.Just like its gas-powered sibling, the Audi Q5 PHEV has quite the litter of competitors. The Audi offers more power than the BMW X3 or Mercedes-Benz GLC-Class plug-in hybrids, but both beat its on-road efficiency. If you prefer some domestic-flavored electrons, the 2021 Lincoln Corsair Grand Touring PHEV is brand-spankin'-new and quite appealing from a luxury standpoint. There are also full-on EVs in the same size segment, like the and the upcoming Mercedes EQC.It should surprise nobody that the 2021 Audi Q5 PHEV is an excellent electrified crossover, blending all the good bits from the internal-combustion Q5 with an electrified powertrain that can drastically reduce a person's reliance on hydrocarbons. If you want to live out your commute in anonymous silence, the Q5 PHEV should absolutely land on your list of cars to test-drive.