degradation

I have a 2018 Ampera with a sudden drop in kWh. Charged the car with hill top reserve (around 80%) and then drove 5 days, spending 18,8kWh according to the infotainment screen, while "fuel gauge" was at 25%. 55% of the battery was spent on 19kWh and that should have been around 30kWh. I do have...