I have had the extended battery for a few months now on my rezound. I start my day around 7am checking email infrequently until about 9am. I have set my email accounts' (4 of them) send receive frequenecy to every 2 hours since I am at my desk all day and dont need to get my mail instantly on my phone. I also have the brightness turned down while I am at work. I have installed the "Advanced Task Killer" app as well. Even with all of these settings, my phone (almost like clockwork) is at 8% battery by 4pm. I am not "hands off" all day, but I do use my phone to play a couple of rounds of Words With Friends, maybe check my FB updates a couple of times, troll the internet 2 or 3 times during the day (for google searches) and that's about it..by by 4pm my battery indicator is red and the phone dies by the time I get home by 5/5:30.
Oh, and yes, I charge my phone all night with the wall charger so I start my day at 100% battery.
Any advice would be appreciated!