My source was a government site, make of it what you will. I may have worded it more strongly than I should have. https://www.fueleconomy.gov/feg/hotweather.shtml

Consumer Reports did a study on this and it only reduced gas mileage by 3% on a Honda.

https://shop.advanceautoparts.com/r/advice/car-maintenance/c...

At 65mph and ~85 degrees. The page I linked sources several studies testing at many other temperatures and speeds.

No car takes a 25% hit from the A/C in gas mileage.

>The internal combustion engine (ICE) variant has an estimated fuel efficiency of 14.7 mpg‑US (16.0 L/100 km), decreasing to 8.6 mpg‑US (27 L/100 km) when the air conditioning is on.

It may be a “worst case, only when actively cooling at maximum power” figure. In reality you’d expect ambient conditions to make a big difference to aircon energy use.

I feel the same way. I've never had a vehicle that consumed more than 5% extra with A/C. With my current diesel I can't notice a difference at all.