I have a screen shot of the Maxx. I can confirm with mild use I got a good 1 & 1/2 days out of the phone.
I pulled it off the charge Saturday morning at 8am didn't put it on the charge til tonight at 8:30pm. NO charging of any kind in-between.
I used some internet radio, slingbox type app and phone calls. Now what made this possible was a mix of Juice Defender and Tasker.
JD was setup to turn data off when the screen goes off on all but a few internet and tv streaming apps that i white listed. Also I kept the screen off alot when streaming internet radio and on the phone. I also have timed profiles set in tasker (guess I could use Smart Actions) to enable WiFi and disable 3G after 8pm and not to reverse it until 8am the next morning. I also have Tasker set to go into Airplane mode at midnight to 7am the next morning.
All of this enabled me to do well beyond the "21 hours" quoted. Of course that 21 hrs was for talk time with phone calls. But I like knowing that now if needed I CAN go a solid weekend WITHOUT needing a charger. I can see lots of goos reasons for that. Like if I wanted to go camping or had a power outage.
Simple things like disabling the data when not being used keeping the display off when the phone is not being interacted with. I can understand if the display is on alot or the phone is doing very processor intensive things or data is being used alot the battery will drain quicker. But it's nice to know it won't likely happen in under 12 hrs.