Where I could get 5 hours use and 12 hours standby now, without modyfing anything the phone lasted 3 hours in use and 12 in standby. I now tried a reset and I am charging from zero. Let's see what happens. One thing for sure, I had to turn off every feature including transparency to get a decent behaviour. At this point I think I could get back to iOS 7.1.2 (don't tell me I can,t, I can) as I am not getting anything new and relevant with 8 anyways.