Most ice cars today have compressors with mechanical shaft seals that leak refrigerant all the time and most mechanics can do a good job at guessing how much refrigerant to add with a little experience. But with our hermetic or semi-hermetic compressors which are completely sealed, weighing in the charge with the factory recommended amount is usually the best and most efficient. That's one of the beauties of our electric cars.
An ev usually has over 300 volts available to drive the compressor, where as, the ice car only has 12 vdc available, thus the need for a rotating shaft seal, magnetic clutch, belts, etc. to drive the power hungry compressor. Can you imagine if they put an ice style compressor on an ev? It would never get to turn at stops or when sitting in traffic, etc.
My wife still occasionally drives her 2003 Explorer dinosaur and I have to add refrigerant about every two years. I don't care how accurate the charges is because the refrigerant is always slowly leaking out so it's never going to have the most optimal charge anyway. The whole vehicle is so hugely inefficient plus it has all that glass; most cars are a rolling greenhouse on wheels anyway.
2012 ES, Cool Metalic Silver, no quick charge, no fog lights and no navi but a cold weather package for when it gets 13 below, wait - it never gets that cold here.