Nothing.... I´m so swamped with work that I can only switch on the camera and shoot meaningless crap in between in my studio. (and get annoyed when the fan kicks in).
So far, I can´t imagine using an on camera mike and having the charger as my power source. I dont even have to record anything to come to that conclusion. Maybe in silent mode, but then the fan goes up in standby - and that *is* loud enough to go on my nerves.
Another thing: I can imagine some embarrassing situations when you switch on the camera after a battery change - and the fan goes into take off mode for 15 seconds.