5D Mk III battery going flat
Have a strange problem with my 5d Mk III.
Normally leave my camera on with a 24-105 kit lens attached without any problems. Set up for a shoot on the weekend and left my 70-200 2.8 mkII on the camera overnight and the battery was dead flat the next morning. I have done a few tests since and found it is only when the 70-200 in on the camera, the battery will go completly flat in about 6 hours. No problem with other lens and also no problem when the 70-200 is on a different camera. Also the problem does not happen every time. I have eliminated the chance of buttons being pressed when in my camera bag.
Any help or ideas appreciated.