Xperia Z5 :: Battery Draining While Sleeping

I've been loging battery performance for a while, and I've noticed that there seems to be little variance between drain while in use and drain while sleeping.

Last night my battery dropped over 50% from 100% without any [major] on screen time. The phone was totally disconnected from any radio interfaces, and everything should have been sleeping.

I do have a white list to alow my smartwatch 3 to work while the phone's asleep, but these are things like Google services.

The battery stats for the period when the battery dropped shows;

Android system 10%,
Android OS 7%
Cell Standby 3%
Screen 3%
Phone Idle 2%
Media server 1%.

I don't really code that much anymore, but if this where a system I was debugging I'd be suspicious that Android Systems and Android OS are using such a big chunk of power while the system should be asleep and waiting to be activated by the only remaining interface, the cellar connection!