This has to be one of my favourite features of iOS8.
It has been a while since I did upgrade but since I have I have noticed my battery life on my iPhone 5 is a lot worse
With the feature I have been able to see there were a couple of apps that were background refreshing and I didn't even use the apps any more, so they were removed which helped a bit. So if you are wondering what is using all your battery it may be worth having a look. It is good to see how much apps like Messages and Whatsapp actually take.
To find it go to
Settings > General > Usage > Battery Usage.
I am always interested in your thoughts so if you have any comments or feedback then please feel free to add any comments, or you can mail me here.