I got SICK of a dead battery by 6PM every night (Nokia ICON), Checked all background tasks, trimmed EVERYTHING down accept for 2-3 apps that I have always had on 8.1. On 8.1 with the SAME configuration, same background apps, I would go to bed with 30-50% battery life left (down to 10-20% if I got heavy into a game or streaming video for like a 1/2 hour).
Last weekend I did a hard reset, and over all this weekend it's been impressivly better. Last night I went to bed, after a long day of texts, emails, twitter, facebook, with bluetooth on, at 11pm, my battery was a 30%... Impressive. With this use I would normally have a dead battery by 4-6pm...
The KEY thing with a hard reset to see an advange, is to hard reset and DO NOT RESTORE. Manually setup everything. Texts came back for me, so it's not a worry.
No question, its better but, still only 70% of what 8.1 was.... If you still have a problem, carry a battery pack with you, or roll back to 8.1