Likely something has started using CPU cycles. You should check the CPU usage for each app for offenders. High CPU usage = fast battery drain.
To get a detailed look at what's happening, try this: Install System Panel or OS Monitor. Tools like these make basic trouble shooting of a sluggish device, battery drainage and some other problems fairly simple. They give the basic information you need.
With the phone at idle (apps can be open, but nothing such as an active game or file transfer) check CPU usage. Normally, idle CPU usage should be less than 10-15%. CPU clock speed varies but should be something less than max. If CPU is high, look at the app list and note the name.
Try disabling or uninstalling non-crtical apps that show high CPU usage and see if that makes a difference.
If you have any task killers, RAM memory optimizers/boosters, battery savers/repairers, cache cleaners, etc etc uninstall them immediately! None of that stuff is necessary. They are counterproductive, waste power, disrupt system processes and degrade performance. Just take a little time to configure your phone properly for your uses. Use common sense. Gekko's list:
http://forums.androidcentral.com/showthread.php?p=4627033
...has a lot of good suggestions, but by no means do you need to use all of them.
Android since v1.0. Linux since 2001