@Kopkiwi
My wife uses her phone to listen to google play music while at work. Shes there for about 8-9hours so its playing music, and using wifi do download it. She also uses google maps on the way there and on the way home so another hour odd. She normally comes home with about 30-40% battery left.
I work in a big steel box (a ship) so im in and out of reception all day so the phone is constantly searching/and or has very poor reception, and its sometimes connected to the wifi network depending on where i am. Today i rode my bike home so i had the strava app open on the way home recording the ride, and have played games a bit along with about an hour browsing the web while listing to music off the phone.
Im still on 50% battery. it really is impressive.
There must be an app that is stopping the phone from dozing or sleeping.
in the battery usage details area of settings, it can tell you over an hour period which are the 5 highesrt users of the battery and how much they have used
see here (click to make bigger):