What Does MHEV Stand For And How Is It Different From PHEV?

Between governments pushing for a ban on pure internal combustion engines and consumers vehemently resisting, hybrid vehicles provide a happy medium for those who aren’t ready to go all-in on fully-electric vehicles just yet either due to preference for ICE-powered cars or concerns like range anxiety or huge upfront cost. If that’s you, and you’re currently searching for information on hybrid cars, you’re likely to come across acronyms like MHEV or PHEV. MHEV is short for mild hybrid electric vehicle, and it refers to a car that pairs a battery-powered electric motor with a gas or diesel engine to assist the engine while driving or restarting, improve fuel economy, and reduce carbon emissions. Mild hybrid cars don’t charge from external power sources like wall sockets or charging stations. Instead, they rely on regenerative braking to charge the battery as you drive.

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PHEV, on the other hand, stands for plug-in hybrid electric vehicle. Compared to MHEVs, PHEVs typically feature a rechargeable battery pack that can be replenished by plugging the car to a wall socket or charging station, much in the same way that you would an EV (electric vehicle). PHEV batteries are usually larger than MHEV ones and can power the vehicle on all-electric mode alone, mostly from 15 to around 93 miles, depending on the car in question. Once the battery feeding the PHEV’s electric motor is empty, the car automatically switches to the gas or diesel engine for seamless operation.

[Featured image by Ralf Roletschek via Wikimedia Commons | Cropped and scaled | CC BY-SA 3.0]

A full hybrid — also known as HEV (short for hybrid electric vehicles) — is different from a mild hybrid car, in that, in addition to supporting the combustion engine, its electric engine can actually drive in EV-only mode, usually at low speeds. During this time, the gas engine is shut off to save you fuel. However, when you reach certain speeds, the internal combustion engine automatically kicks in, working alongside the electric motor to supply extra power to the wheels. Note that the speed at which a full hybrid car switches from pure EV mode to engine and electric power can vary based on the model and battery charge level. 

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Some hybrid cars typically start using their gasoline engine from around 15 mph, while others run at speeds over 35 mph before requiring the engine to come into play and help provide enough power when accelerating or climbing up steep grades. The electric range of HEVs typically vary from 1 to 3 miles. MHEVs and HEVs have shared similarities, however, as they both don’t have an external electric grid charging feature. Instead, HEVs use their gas-powered engines as well as regenerative braking to recharge their batteries. 

Plug-in hybrid cars usually cost more than mild hybrid ones due to their larger battery pack and more powerful electric motor. For example, the Lexus NX 350h AWD, which is a mild hybrid, has a starting MSRP of $46,300 – meaning it is priced $15,115 lower than the plug-in hybrid NX 450h+ AWD, which has a sky-high price tag of $62,415. But while that those prices highlight the significant difference in cost between MHEVs and PHEVs, it is due to more factors than the more robust electric engine alone. For instance, while the 2025 Lexus NX 350h AWD features a 9.8-inch touchscreen infotainment system, the plug-in hybrid NX 450h+ AWD goes bigger with a 14-inch infotainment system. The NX 450h+ also comes standard with a heated steering wheel and a power moonroof, which are optional on the mild hybrid NX 350h. 

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As for performance, the 2.5-liter, inline-four plug-in hybrid engine in the Lexus NX 450h+ makes a whopping 304 horses, while the 350h’s 2.5-liter in-line 4 hybrid mill gets a combined 240 hp. This results in a 0-60 mph acceleration time of 7.2 seconds for the NX 350h AWD, NX 350h Premium AWD, and NX 350h Luxury AWD. The performance-focused NX 350 F Sport Handling AWD, for its own part, sprints to 60 mph in a 6.6 seconds, which is about 0.6 seconds slower than a NX 450h+, which requires 6 seconds flat to get to the same speed. However, the NX 350 F Sport Handling AWD is faster than the NX 450h+ by top speed, as it can reach speeds up to 127 mph, whereas the NX 450h+, like the rest of the 350h models, has a top speed of 124 mph. 

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Predictably, the Lexus NX 350 F Sport Handling AWD’s higher performance means fuel economy suffers, with the performance model returning 24 mpg of combined fuel economy, while the other 350h models gain 39 mpg. As for the NX 450h, Lexus estimates its MPGe (miles per gallon equivalent) to be 84 for both the standard NX 450h+ AWD and NX 450h+ Sport Handling AWD. The PHEV can drive on electric-only range of up to 37 miles. 

Ultimately the question of which to buy comes down to personal preference. If you are looking to do most of your short trips on only electric power with a zero-emission vehicle to minimize environmental impact, then a plug-in hybrid model might be right for you. Most PHEVs deliver up to 35 miles of electric-only driving, which is suitable for short-distance driving and can cover your short commute without using the gasoline engine. However, if you want to kick things up a notch, there are plug-in hybrid cars like the Mercedes-Benz S580e that give you up to 58 miles of electric-only driving, BMW 530e (64 miles), Mercedes-Benz C300e (68 miles), Mercedes-Benz GLC 300e (76 miles), or even the Polestar 1, which offers up to 93 miles of range.

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PHEVs are also ideal if you want a car that’s loaded with all the bells and whistles, as plug-in hybrid models typically only come in higher trim levels that bring more niceties than a MHEV has. That being said, PHEVs come at a price, and a very hefty one at that. If you can’t afford that higher purchase price or do not see yourself being able to charge up the battery as frequently as required, then an MHEV wouldn’t be a bad idea as the more energy-efficient transportation of choice, as it is cheaper than a PHEV and doesn’t need to be plugged in to charge.