Hi. I'm new to the Mavic coming from years with DIY quads and RC planes.

Is it normal for the battery to drain fairly quickly while the Mavic is on but sitting on the bench?

While setting it up for the first time tonight , it was on but no motor action or video recording. (The camera was transmitting, though) After about 20 or 30 minutes the battery had gone down from 100% to 75%. This seemed fast to me since it wasn't flying, but like I said, I'm brand new to DJI and the Mavic. I have no idea what is normal. Thanks for your help.

Yes, that is normal. In fact if you're on a situation (while flying) where your battery is tight to come back, stopping the recording also gives you some extra time in air.