I've had a lot of WP devices over the last couple years, and ever since the upgrade to WP8 the battery life has been inconsistent. I've had 3 different 920s and 3 different 925s and found that both phones had periods where the battery drain was anywhere from great to disappointing to disastrous. I think this is either a universal Nokia firmware issue or a Windows OS issue.
I typically use my phone in a light-to-moderate fashion. Lots of email (Outlook.com and Exchange), ~1 hour of calls, couple dozen SMS texts, handful of photos, Twitter, Facebook, Reddit and news apps. Very little IE usage, and zero games and only occasional navigation/mapping. I live in a strong, re-farmed LTE area for T-Mo. I rarely stream media, and when I do it wipes out my battery badly. I typically have BT, WiFi, LTE and Location on all the time.
With these settings I find that some days I'll get 1.5 days of power. Other days I'm lucky to make it to 8PM. Some days things will go haywire and the phone gets super hot and the battery wipes out completely in just 2-3 hours. I've tried managing my background tasks and turning off WiFi, location and BT but nothing seems to matter. I haven't been able to effectively tie the issue to any one use case. My theory is that the LTE radio sometimes just craps out and starts heating up. Either that or I'll be in a spotty WiFi area and the phone is constantly searching/connecting and failing without falling back to LTE as it should.
Also, streaming music and watching streaming video are brutal on battery. This is to be expected, but I find that the phone gets unreasonably warm with the video and the phone seems to not cool down after I stop. If my theory about the radio's issue are incorrect, it's probably just a issue with the way WP8 handles task management and tomb-stoning.