What I cannot understand surely on an electric car the radio heated seats etc are using power from the batteries so surely that reduces the range especially in winter with your heater on etc ! So say a range of 300 miles is 250 miles realistic ?
Trick is to preheat your car in winter whilst tethered to the mains electric, other than that you’re right, range drops if you switch anything on. Some EVs have a heat pump which helps with more efficient heating but heat pumps become less efficient with lower temperatures (they work great for aircon in the summer & not bad for heating at 10C in winter, but at -10C they’re inefficient and will use a lot of power from your range).
Range is also reduced in winter by the battery temperature, a cold lithium battery will hold 20% less energy so your range is hit again. You can see the difference in real world cold & mild conditions in https://ev-database.uk/car/1168/Peugeot-e-208 as an example.