IMHO, battery life on my iPhone 5 is noticeably worse than it was on IOS7. Looks like something they will fix in 8.0.1.
I’m sitting here, watching the battery monitor drop by 1 percent every 5 minutes as I use it.
Battery life issues seem to be endemic to .0 releases.
Odd. On my iPad Air, I was observing yesterday it seemed slightly better. In fact, mine is sitting at 55% right now, when normally, after a day of normal usage, it'd be close to 15% by now. I've noticed the screen brightness is more adaptable to ambient light than I've ever seen it before, adjusting the brightness and contrast in response much more quickly and more frequently than ever before.
The iBook app now switches to a "night" view in low light conditions automatically. . . and I wonder how many other apps are similarly switching. It seems, at least on my iPad Air, to be saving battery quite well. Perhaps other iOS devices may not be working so well with this "improved" functionality?
On the other hand, the Ars Technica thurough review reported their tests showed virtually no differences on their various test models of iOS devices between iOS 7 and iOS 8. Go figure.
I did have some issues with FR website links being non-operational just after my upgrade. Everything became copacetic after a cold restart. . . But I did my cold restart before I had a chance to see if I might also have had any battery draining issues at the same time. Cold restarts is what the Genius Bar recommends as a first step that sometimes handles battery issues on new version upgrades, so I'd suggest that. Let me know if it works.