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Ask a Mechanic.....EV battery range degradation

Today we’re discussing plug-in hybrid and EV differences.

Every week, we answer your questions about what is going on with your vehicle. Today we’re discussing plug-in hybrid and EV differences.

Dear Ask a Mechanic,

I recently purchased a (Toyota) Prius Prime, the kind that plugs into your house, with the assurances that it had a range of 1035 kilometres.  I have been very disappointed to discover that 995 kilometres of this range is gas powered.  The electric range of the car is 40 kilometres. I have a feeling that many people will be, like I was, ignorant of this fact.  However, the Prius does boast excellent gas mileage (mine shows 3.3 L/100 km), so I’m wondering if there’s an aspect to hybrid electric motors that I don’t understand. – Feeling Fuelish

Any confusion about what the various types of hybrids, battery-electric vehicles (BEVs), and range-extended BEV models are and how they work is understandable.

While these vehicle types all have in common electrification and the substantial efficiency gains of recapturing energy during deceleration or braking, there’s a lot of misunderstanding about the differences, particularly between plug-in hybrids and range-extended electrics. I believe that’s what caught you out.

Generally, the following definitions apply:

(Non-plug-in) hybrids combine two sources of motive power, normally an internal-combustion engine (ICE) and one or more electric motors, either of which are capable of propelling the vehicle individually or together (unlike so-called mild hybrids, whose motor can only restart or supplement their combustion engine). Their on-board battery is recharged solely through energy recapture or by the ICE through the hybrid system. The regular Prius is a familiar example.

Plug-in hybrids (PHEVs) add to the hybrid design a larger capacity battery and the ability to charge it from an external power source. The additional energy storage allows for a greater amount of electric-only operation, and the electric motor(s) is/are usually more powerful than those in a comparable conventional hybrid to improve electric-only speed and acceleration capabilities. Even so, the vehicle is still primarily gasoline (or diesel) powered, and most of its total range is provided by that fuel. If never plugged in, they would function indefinitely as a regular hybrid. This is the case with virtually all PHEVs, including your Prius Prime.

Battery-electric vehicles are self-explanatory – there’s no internal combustion or alternate energy source; power and propulsion are entirely provided by one or more electric motors drawing from an on-board battery that is recharged from an external source. Think Teslas or the Nissan Leaf.

Range-extended BEVs operate primarily as a BEV does, but also have an on-board generator – usually a small gasoline engine – that unlike in a PHEV is not mechanically connected to the wheels, but instead can provide electrical power to the motor(s) or recharge the battery to increase range. BMW’s i3 REx is one of the few mass-market models using this configuration to date.


Ask a Mechanic is written by Brian Early, a Red Seal-certified automotive technician. You can send your questions to These answers are for informational purposes only. Please consult a certified mechanic before having any work done to your

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