My thunderbolt has been unplugged for over 12 hours today and is at full charge. I had very little usage, but it is on and is on the 4g network all day. I texted a little and that was about it. I did change all of the settings as has been suggested. If you do a google search and adjust the settings your battery will last properly on this phone. If it is dying immediately...it is because of the settings, or your phone is defective. No smartphone with all settings maxed, everything synched, and everything used constantly will last. At the very least turn your screen way turn, turn off navigation when not using them, check apps that are running...I had Grubhub running on navigation (and I am new to Droid and had no idea that it was even on.) It was consuming 21% of the battery. I didn't even know it was on. I killed it and turned of the nav. The screen is very bright and comes default at like 50%. Turn it down to like 20%. Tons of other things, like the default auto sync and such....
Oh, and when I say little use...I wasn't including the music usage. I probably got a solid hour of music in there as well.