I second Obvious' thought.
You could also bring it in to a Sprint repair store for them to test the battery and phone and perhaps get a new battery if yours is bad. Be prepared for them to do a hard reset. You could even do one and see if that helps to save your self a trip (which would clear your phone of any third party program you may have installed that may be constantly running and draining your battery.)
Additionally, you could try more battery saving tips like those listed in
Kabuk1's battery life tips! which could help (even though they are for the Pro).