Review: Samsung A900

Each software release addresses a few things that have improved battery life, so if you are having an issue, update your software:
Menu: Settings: Others: Update Phone Software.
(you have to have at least two bars of battery to do this, and can't be connected to a charger.)

If this doesn't help, do the above steps, and also try to turn off service light, put phone on Sprint Only mode, and there is even a power save mode that does most of this in one step.

It's a small phone, you trade size for battery life. Rich or whoever did this review was able to attain a day plus in testing, and most people charge the phone every night.