What's the fuel efficiency of a plug-in hybrid when the battery has run out?

Is there a rule of thumb about how much less efficient a plug-in hybrid is when the battery runs out compared to a combustion engine equivalent? For example, if a conventional petrol or diesel model did 40mpg on the motorway, would a PHEV version of the same car (with its extra weight) get, say, 36mpg - i.e. a 10% drop? Do you have any guidance? Thanks.

Asked on 19 July 2021 by slyb123

Answered by Dan Powell
PHEV (plug-in hybrid) cars are not designed to be driven without a fully charged battery. However, in my experience, with the Volvo XC40 PHEV, fuel economy can drop by more than 50 per cent: www.honestjohn.co.uk/our-cars/volvo-xc40/what-happ...d
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