How do you get to that display? In the battery section of settings I still only see usage and standby numbers on my 5 running official release of iOS 9.0 so is this screen time in some other section of the Settings app?
I'm with you on the "ghost usage", I've even came up with a very similar term to refer to it ("phantom usage" in my case). I see it a lot because I only tend to use my phone when I'm out of the house and recharge it every other day so if I'm in working at home for a day it's not uncommon for my phone to show 24 hours of standby and something like 3.5 hours of usage even though I've never touched it for the whole 24 hours. I have background applications disabled, have location services off for all system activities, don't have iCloud or email set up, and have calendar and contacts set to manual fetch. I just do not understand what can be chewing up all that time on an iPhone that should literally be doing nothing except maintaining a connection with the phone mast (WiFi and Bluetooth also off and things like App Store told not to use mobile data).
My excessive phantom/ghost usage is on earlier iOS releases. I haven't had a chance to see what happens with iOS 9 because after my upgrade I did have a lot of real usage from playing around with the new release. I'm leaving my phone untouched for 24 hours now and am hoping that iOS 9 will be better but I'm not so hopeful based on this thread.
When Apple spoke about gains in battery life I was wondering whether a lot of that claimed gain was going to come from its developers hunting down where iOS unnecessarily woke up the phone to do housekeeping and generated this phantom usage. In my case I really do think it's iOS itself that is doing it because I've also tried killing all the apps from the multitasking screen before leaving my phone idle for 24 hours and I still get 3+ hours of phantom usage.
Oh, I usually do refer to it as phantom usage
I ran some XCode Instruments to see process activity in iOS9, and it seems backboardd never sleeps when the phone is on standby - it idled between 0.5 and 1% usage, which adds to the CPU time non-stop. Interestingly this non-stop usage seems to keep other system processes running at 0.1% usage - all in all around 10 processes at 0.1% each, so we have around 2-3% cpu usage in idle. In comparison on 8.4.1 backboardd will idle to 0% with only small spikes between 0.2% and 0.3%, which briefly pulls other system processes into use at 0.1% - the CPU time doesn't constantly rise though.
The most common phantom usage bug I have encountered is mstreamd (related to iCloud Photo Stream). I would credit myself to finding this, but there are other people that noticed this too -
My Original post -
https://forums.macrumors.com/threads/ios-7-1-battery-drain-merged.1715396/page-3#post-18882778
More technical people discussing it (MacRumors isn't famed for it's technical expertise) - -
https://www.reddit.com/r/jailbreak/comments/28n3vn/solved_crazy_battery_drain_may_apply_to_other/
Some other guy's XCode logs -
https://discussions.apple.com/thread/6492952?start=0&tstart=0 (sadly the "expert" at the Apple site gave some typically useless advice for a question far beyond their technical knowledge)
A tl;dr mstreamd basically starts and stops in an endless loop regardless of whether Photos is enabled in iCloud, and can even persist with iCloud entirely removed - this causes a lot of phantom usage as the phone basically never sleeps as a consequence.
Sad thing is - this has been around, documented, discussed, for well over a year (year and a half since my original post), and it still exists (I'd be willing to bet it exists in iOS9).
I'm also willing to bet this mstreamd bug is the cause of a great majority of people's hot phones/terrible battery/lagging.
Before I get jumped on by Apple apologists - go download XCode yourself, and run Instruments process monitor.