Unless you have your phone set to have it's radios active (WIFI and BlueTooth) when they aren't in range, this can seriously suck the power.
I have a new BlueTooth headset (stereo) that I use for music, with which I listen to music with my Touchpad. I had connected it with my phone (but still using it with my Touchpad) and within a few hours, it had sucked my battery dry. Just that it had been paired to it, I believe that it was trying to communicate with the headset and since the headset was communicating with the Touchpad for the music, it made my phone "yell at it".
I unpaired it (removed it from the phone), but found that as long as it's within range of this headset, it kills the battery. So now I turn off BT on my phone when I listen to music via my touchpad with these headphones.
So.. I'd say, check if you might have something similar that might have been added in your environment... a WIFI network/router, some BT devices... anything that might be pinging the phone.
This includes checking if you might have some settings that's changed.. the GPS (should be off unless using apps that need it), and having your account updates (emails) set too high.
As far as I know, the battery will get sapped faster depending on the connection it's got to either your provider (cell phone tower being too far), WIFI and BT devices.
So unless you have downloaded a new App that might be running in the background.... I've personally notice a difference with my Pre2 lately after I downloaded a few games, Monopoly being the worse one that makes me wonder the most. Don't know why, but only since I've installed this game, did I notice my battery going dead a lot faster than before.
Otherwise, after 2 years, the battery might just have kicked the bucket and a new one needed.