I read through about half of this thread yesterday as I was only getting about 8hrs of battery life. Here's what I did last night, not promising it will work for you, but it's worth a try:
Drained my battery to 0%. Ironically, had to run Netflix for 2 hrs to lose 30%.
Let the phone shut off by itself. Turn it back on, it shows a battery symbol, then turns off again. Battery totally drained, right? Wrong. Don't charge it yet.
An hour later, turn it on again, mine booted up, showed 0% battery, then stayed alive for another 90 minutes! Had to run Netflix to get it to die.
This time, turn it on again, it'll vibrate but not turn on.
Wait another hour (no rationale, this is just what I did)
Plug it in overnight and let it charge. This time I also used the official Nokia charger which is 1.3A, before that I'd been using a 1A Palm charger. I noticed that it got to about full charge in just 3hrs! I also disabled NDrive and Weather Channel background tasks. NFC always off, Bluetooth always on.
So far I've gotten through 4 hrs of medium-high usage (4 push email accounts, auto brightness, listening to podcasts via bluetooth, WiFi always on) and am at 87%. I'll update you guys on how long I can go throughout the whole day, but this is definitely better than yesterday, and I think my battery issues are over. Estimated time left: 3 days 10hrs, lol.
It's weird that my phone turned on after being dead and stayed on for almost 2 hrs!
I think there's certainly a calibration issue here...
PS. I also want to try a hard reset, but haven't figured out how to backup my start screen layout... tell me if you know!