Extra gas cost for charging while driving on highway on empty battery?

[Carmageddon]

Hi, I am very happy with my "new" 2019 Outlander PHEV 2.0 liter (North American/Canadian edition)!

Here's one thing my uncle claims and I don't know how to respond to:
He says that whole the engine is charging the battery and powering the wheels at 120km/hr, might be as well charging the battery - the engine is already doing the work.

My rational says it'll take extra fuel to rotate even faster , but then how could it be, if it needs to rotate the wheels at specific RPM range anyway as it doesn't have a transmission...

Has anyone checked, is there an extra gas to charge battery to full while driving on the highway? And if so what is delta/differencial?

 

[Lon12]

Yes. Unfortunately there is no free ride or perpetual machine under the hood. I’ve never looked at the delta but you can watch your consumption increase when charging.
When driving in the Mountains I always leave it in charge mode so that I can maintain 120 kph going up the big hills. I also try and keep some battery available for driving through towns with traffic lights. Hate idling when stopped.

 

[greendwarf]

Just to add to the previous post - it doesn't "have to rotate faster" but the more energy you take out (i.e. forward motion plus battery charging), the more fuel (i.e. energy in another form) you have to put in to keep it in balance - so your consumption increases to maintain the same road speed when charging, otherwise hitting the Charge button will slow you down. It's all just a matter of physics.

So, unless you need some battery, as described in the previous answer, don't bother because it is likely to be way more expensive than plugging the car into your domestic supply, when you get home.

 

[jaapv]

What Lon12 and Greendwarf said. It is all much of a muchness - the charge and save buttons are there to allow you to "predict the future" to the car's computer. It can never know whether you will be doing a stretch of driving which can be done more efficiently on battery power ahead.
The main thing is to make sure that you arrive at the next charge point with an empty battery and to remember that it is more efficient to drive on electric power under 80 kph and more efficient to drive on fuel over 100 kph.
As for the consumption vs rotation: just think of a conventional car: when dragging a trailer or going uphill, you have to depress the accelerator deeper (i.e. feed it more fuel) to keep it at the same rotational speed.