Well actually my Lumia 520 is also facing battery drain( both during Developers preview and during Cyan, Update1 ) and so is my brothers Lumia 620 (Cyan without Update1) .
Battery saver app showing 1 day 15 hours does not actually say anything decisive regarding battery life. It does not mean that you will actually get 1 day and 15 hours. The overall standby time may have increased, but come on we haven't bought a smart phone to keep it in standby :/ :/ . The active usage time has decreased a lot. For e.g surfing internet in WP8.0 (continuous) used to give me 5 hours now its about 2hrs-2hrs 20 mins atmost in WP8.1 :/ :/
Whenever I turn the screen on and use the phone battery drain sky rockets whether its the internet or Whatsapp or just surfing through photo gallery :P :P Strangely enough the battery saver app always shows "Phone" at the top :( :(


Just have a look at the screen shots. The l520 was charged to 100% at about 10.30 pm and in the morning at about 9.30am it was at 93% (idle usage was nil almost, wifi was on throughout) and then in the morning I checked the WhatsApp messages, a 2 minutes phone call, 8-10 minutes checking headlines in the News app and the battery is at 76% now :/ :/ Now that ain't even a heavy usage :/
Sorry for the long monotonous post though :P