So I got a Lumia 925 last week, and I've had to charge it up to three times a day because the battery drains so quickly. It is also constantly warm, which makes me believe it's an app running in the background.
Even while charging, it takes up to five hours to charge instead of the usual two or three. In the last seven days, there was only one charge which completed in two hours' time (this is how it should be), and the phone wasn't hot as it seems to usually be while charging.
I've tried rebooting the phone in case the process is killed, but restarting doesn't do anything. Another oddity is that even switching Battery Saver on doesn't help. Battery Saver is supposed to allow apps only in the foreground, isn't it?
I'm now in the process of going through my list of applications under 'Background tasks -> Advanced' uninstalling them one-by-one to see which application (if any) is the culprit; this'll take a while. The same apps are installed as were on my HTC 8X (and battery life there was excellent), so it's either an app not playing well with GDR2/Amber or it's a Nokia application causing the problem.
Here's a screenshot of my phone about 30 minutes off the charger:
http://imgur.com/W24dZp0
Edit: Hmm. Something interesting: if I switch Battery Saver to 'Always on (not recommended)', and restart my phone, the megadrain stops. So this is perhaps an app/process that starts when my phone boots but doesn't stop when battery saver is turned on, unless battery saver is on when the phone boots, in which case the app/process doesn't start in the first place?
Edit 2: This is reproducible and a temporary solution (I can't always be on battery saver after all): the phone is stone-cold (room temperature, actually, but the cold metal feels great) after I unplugged it from the charger, switched on Battery Saver to Always On, and restarted.