My biggest battery drain is with the Store when trying to get updates. The Store also has errors with 7 apps that cannot update, but there is no place on the phone to delete them. Two of them don't have titles so when hitting the X the Store app closes instantly. I did an install of 10586 from 8.1, then did a hard reset, imported no data, and used only the standard apps, removing those I don't use. The phone is a Lumia Icon. Also, with no background activity running, just sitting for 24 hours drops the battery by 40% and that is with no messages, no calls, no emails. Drain is still an issue. No replies to tweets, and of course no replies to "Feedback" posted. It is a test phone so the only downside so far is the monthly line fee from Verizon ... and my needs are met by my primary iPhone 6+.