I had my Chargemaster unit installed late last year and this monitoring feature was one of the various extra-cost options you could have - definitely not a "hidden" feature at that time. I did not go for it as I can see roughly what I am using from my home energy monitor anyway and at the end...
It seems to me after several months of ownership in the UK that the 2 factors which most affect EV range are temperature and speed. I agree that if you mainly drive gently and below 50mph (80kph) the range achievable is close to the advertised one if the temperature is not too low. Recently...
I have just got this working using a vGate iCar 4 BLE which I got for £27 on Amazon. It seemed to need a "kick" to get it working properly by running an OBD test on it but since then has been fine.