This derivative has a whole clutch of sector rivals who, at first glance, seem to use much the same engine technology, so you might not expect the same kind of efficiency advantage in-segment that the more affordable RX 350h self-charging Hybrid model enjoys. Well yes and no. The RX 450h+ has a smaller 18.1kWh battery than some of its competitors, hence a 43 mile EAER-rated range that's 17 miles down on the class leader in this respect, the Mercedes GLE 400 e. With that Mercedes though, as with other similar PHEVs in the class like the Jeep Grand Cherokee 4xe, the Porsche Cayenne E-Hybrid and the Volkswagen Touareg R, the difference comes when you run out of EV range, as of course, beyond the city limits, you inevitably quickly will.
At that point, in all the competitors just mentioned, you revert to a big thirsty petrol engine. In an RX 450h+ in contrast, you revert to the much more frugal self-charging full Hybrid powerplant of the lesser RX 350h - which, as we've already seen, is the most efficient choice in its class. That's why the RX 450h+ model's 25g/km CO2 figure all-but matches the emissions reading of a Mercedes GLE 400 e, despite significantly inferior EV range, hence this Lexus model's same low 8% BiK tax rating. As with any PHEV, the RX 450h+ model's three-figure combined cycle fuel figure - here WLTP-rated at 256.8mpg - can be taken with a pinch of salt, but 35-40mpg as a regular reading should certainly be well within any owner's real-world scope.
If you've stretched up to the RX 450h+ Plug-in model, you'll want to know about charging it. Charging times are aided by a 6.6kW on board charger, which is why it takes only two and a half hours to replenish those cells from a conventional 7.4kW garage wallbox using a 230 Volt / 32 amp connection. Connect up to a feebler power source like a domestic plug and you're looking at replenishment in 8 hours and 15 minutes - so still comfortably achievable overnight if, say, you happen to be away at a hotel or staying over with friends.