I got same results after couple hours and lost 7-9% per hour(2mins. on-screen). I will repeat it tomorrow, but I wouldn't expect much different results.
edit: I tested it again with same result. Then I switched to power save mode and back to normal and it's gone. Strange.
I found, that I have excessive heating and battery drain too. I picked some data, hope it helps:
It seems, that media_server causing this. All data are picked after reboot with no load or apps running on background.
There was V5, if you don't trust me, install V5 and check it for yourself. Or Google it.
And camera sensor has no processing CPU, all processing is done by ISP, which is part of SoC. BTW IMX214(13Mpx version) is 1080p@60fps capable.