[Q] Battery Going Flat

view story

http://forum.xda-developers.com – Well, I dont use my phone often because I use my Xperia but when I do, I charge it to full battery, then I turn it off, as you do to save battery, but next time a turn it on, it wont turn on causing me to plug it in, and Flat Battery! Do I need a new battery or should I try flashing a new ROM? Thanks! BTW Im using the Factory Battery that came with the phone (HowTos)