This December 2019 video from the USA says about itself:
Biology of bats
It turns out that warm-blooded animals aren’t warm all of the time! Researchers at Brown University studying the muscles in bats’ wings found that their wings operate at a significantly lower temperature than their bodies, especially during flight. The National Science Foundation-funded team says this shows that warm-blooded animals have a lot more variation in body temperature than expected. That has implications for how animals are moving around, including humans.