I have not torture-tested my MG EP (Same as your MG5) to nearly full-flat battery here in Thailand, but based on 1500km of driving and pulling the battery down to mid-20's %, I can tell you that this Thai version can easily get 300km on a charge. Stated range is 380km. This is using A/C all the time... we don't need heat here, but I'm sure running a heater is much worse than A/C, which appears to use only about 400-600w of power on low setting.
Our stated battery capacity here is 50.2kwh.