The absolutely worst efficiency I've experienced was 2.7km/kWh at 120km/h in DS3 e-tense. That was a v1 Stellantis drivetrain, without a heat pump. Peugeot e208, Corsa-e, etc. are the same thing. Stellantis sucks at EVs, especially their first gen, so that's probably really the worst case scenario (apart from EV's nemesis: towing non-aerodynamic trailers at high speeds).

So if you take an EV's battery size in kWh and multiply it by 2.7, that's the worst range you will get in km.

In normal weather EVs get 5-7km per kWh.