There has to be something with the newer cameras that use the transmittive LCD. My 1Dx was sucking battery when asleep AND using excessive battery during single-shot usage. Non-backlit LCDs don't use very much power at all (look at how much battery life comes from LCD watches), it's the backlights that hog power. Nowadays, with LED backlighting, that has even dropped to very little. Despite all that, that transmittive is using power at all times (take out battery and watch the screen tranparency change). But, to kill a battery overnight, the power consumption would have to be tens of milliamps per hour.
With mine, it was something in the firmware that was preventing the camera from going completely to sleep, which was why the camera was chewing battery sitting on a desk asleep. After about a dozen flashes (back to previous and multiple times of the current), mine has resolved both power hogging and sleep usage.
It could have been the meter not powering down or the disk controller remaining idle the whole time. Either way, it's probably more likely that they have switched to using less discrete components and the new SoC is the cause. The new tech is nice because it allows for quick (and previously unavailable) changes and new features, but becomes so firmware dependent that a small bug will wreak havoc and become almost untraceable as there is much going on behind-the-scenes that the firmware writer doesn't know about.
It may also be that the newer Digic processors operate in a multi-state mode, throttling to a lower power with light usage and spooling up to higher bus and clock rates when loaded. If something was idling high and preventing the low power state from engaging, it would have the same effect.
Either way, hopefully Canon'll discover the cause and fix it in firmware eventually. Probably more likely they'll figure out the 7D2 (as there are more of them) first and will eventually trickle up to the 1Dx.