[mindfrost82]

You can check your /Windows/StartUp folder and see if there's anything unusual in there. I haven't used SPB Mobile Shell in a while, but plenty of people do. Make sure nothing is constantly on the internet.

You can search for a cab on here that will automatically disconnect the internet after 1 or 2 minutes of being idle.

Check your backlight settings. Try to keep it in the middle if possible. Check the power settings and make sure the backlight turns off in 10 or 30 seconds to make sure its not on for long periods of time in your pocket.

How is your signal? Unfortunately there's no much you can do if its bad, but if it is, that could be a major reason for battery drain.

If you bought it used the battery could just be worn. They don't last forever, so if its possible to get a 2nd one to try, you may also consider that.