I too have a Lumia 900. Any questions or picture requests, let me know as well. I'll be hanging around trying to answer anything I can legally answer (I love my job and won't jeopardize it with releasing information that is not already public knowledge released by AT&T).
As far as battery, I cannot answer for LTE usage as i'm not in an LTE area... but I CAN tell you that my battery is lasting quite long for me. It's comparable to the Galaxy Note battery. Throughout a day, I spend about 1-2 hours on calls... I text throughout the day, Facebook, have weather updates, use engadget quite a bit, few youtube videos. I also have my screen brightness at full, and so far i've been able to go from 6am till roughly 10pm with 25-45% battery left.