40 EV miles of 70 to 80 mph is good. Can’t expect more than that. Would get more at lower speeds no doubt.
It is nice to know that a dealer would replace the battery, without testing it, simply because an owner asked for a new battery. Unfortunately, you may have just replaced a good battery with another good battery. At the moment it appears that the 12V battery was not the culprit behind this peculiar behavior. I did review some earlier posts and saw your photo that showed 13.7 miles of EV range and the gauge appears to have ~7 bars. You may have already answered this question, does the ICE come on when you are driving in EV with less than 13-15 miles of range remaining? I’m guessing not, since you are getting ~40 miles at 75mph. I haven’t spent 15-20 minutes sitting in the car with the power on and EV at ~15, but I have on numerous occasions driven down to single digits, even zero, on EV without ever triggering the ICE. It really adds to the mystery if the ICE doesn’t come on while driving below 15 but does come on while parked below 15.
The dealership didn't test the battery, but I did have it tested at O'Reilly, where it tested as "Bad Battery." They seemed to take my word that the battery tested "bad." And no, the ice does not turn on with 15 ev miles that I can ever remember.
If you’re getting 40+ EV miles at near 80 mph, count your blessings. The only thing that kills EV range worse than high speed is below freezing temps coupled with extravagant cabin heat.
Lesson: Don't take it for granted that the engine won't turn on randomly. Be vigilant when having car on in an enclosed garage.