I just got my Eris on Saturday...at first, battery life seemed to be OK, even with my 3 year old play some apps.
I charged it this morning in the car on my way in to work (about an hour), and it was still pretty charged before I did that (I didn't check to see how much, but I think it was still a full green bar this morning)...and, I didn't use the phone while it charged. In the past 6 hours, it's gone down to 40% battery life left...I've maybe used 5-8 minutes in calls, received 18 texts (1 of which was a 43KB picture), and sent 13 texts. I played a few games od Flood-It (app), and that was about it. I did have it go a little crazy on me earlier (restarting...), had it lock up on me twice (once had to pull the battery)..............not sure what's going on, but my battery went down WAAAY too quickly today.