Ok, I used to be quite the defender of this phone's battery life- my battery life USED to be great on this phone, and now it's just "ehhh, ok, better than average but not that of a battery with nearly double the capacity of your average new phone"..
Here's what I have on my battery screen on my phone that was taken off charger at 6am and used sparingly today:
50% - Discharging
10hr 11m, 53s on Battery
Screen 61%
Android OS 11%
Phone idle 7%
Cell standby 4%
Voice calls 4%
Browser 4%
Wifi 3%
Google Services 2%
Android System 2%
It just strikes me as odd because I may have used my phone for maybe 45 minutes or so, and none if it involved anything but web browsing and maybe 5 minutes of e-mail reading. The rest of the time, my phone's been in my pocket.
At this rate, technically yes, I will be good til around 10 or 11pm if I use the phone just as I did earlier.. However, when I get off work, I tend to use my phone constantly for almost an hour and a half, using a media player to play locally stored music on my way home from work., reading e-mails, playing games, applying app updates, and such.. So I'm guessing that by an hour or two after I get home from work, my phone will be at around 35% battery left, which is kinda scary if I wanted to stay out late tonight. If that were the case, I'm sure my phone would be powering itself off by midnight- something I wouldn't have expected for a moderate-use day and this phone.
Might be time to do a factory reset and cache reset and hopefully fix this a little.