If you shoot video, you know you're pushing a lot of data around. Knowing just how much data and how much battery life you can expect out of your camera and external recorder is crucial to planning both projects and future purchases. This encyclopedic analysis from Lens Rentals should give you all the information you need.
Shooting video tends to generate multiple gigabytes of data and eat through batteries very quickly, both issues that must be considered when choosing which camera, external recorder, memory card, and codec you're using. For example, recording MJPEG at 59.94p in 4K resolution on the 1D X Mark II generates a whopping 6.7 GB of data per minute, giving you less than ten minutes of recording time on a 64 GB card, meaning you'll want to pick up a bigger CFast card and hard drive.
Lens Rentals did some impressively comprehensive analysis, giving a breakdown of the recording time in minutes per gigabyte you can expect for each camera, codec, and extension combination. They also have the expected runtime of the vast majority of external recorders along with the same recording time breakdown as given for the cameras. To see the full data set, click here.