That can’t be correct. Even my iPhone shows 100% charge when the actual capacity (due to degradation) is around 87%. I think the charge will always indicate 100% regardless of whatever actual battery capacity you may have left.
Temperature is getting colder. The car uses about 6% more energy per 10º F. colder weather not including cabin heat.
Energy (Wh) taken can be accurately measured as can the miles driven. Thus Wh/mi reports are pretty accurate. SoC is difficult to measure. That is why assessing the battery's charge capacity requires multiple measurements over time as discussed extensively in this forum (but not this thread).
I imagine the bigger problem is hysteresis so it is probably wise to try and test the same-ish Soc interval -- say 75 to 25% SoC
Hysteresis is way beyond my pay grade so I'll just post a link
If you go to Setting>Battery>BatteryHealth, it'll show you your current Max Capacity. My 2 yr old iPhone X shows 98%. So, while the front-facing screen will show you've charged to 100% of current capacity, if you look in your settings, and check battery health, you'll see that current capacity is 98% of the original design capacity.
I am having the same issue. I only have 7,500 miles on my car. I use Teslafi. I don't drive my car any different than I did before. It started after the 2019.32 update and has dropped off more with the other updates as well. Monday through Friday I drive my car the same route at the same times. I have 3.77% battery degradation at 7,547 miles. Does that mean at 75,000 miles I will have 37% degradation? I don't think so. The 310 mile range was based on a prior software version. I think the newer version is showing the car being a slight less efficient. So the degradation looks bad. But in reality I don't believe the battery has changed just the efficiency in the way the car uses it. Hope this helps. If you are a data person I suggest Teslafi.
