Have you charged it correctly since getting it? I've had mine for around 3 months now(and a K750i before that) and although I don't use the mp3 function all that much from my normal use(quite a few texts and a few short phonecalls) I get about 4 days battery life between charges if not more. I'd see if your phone does it again, if it does then you may have a faulty battery, not sure if they are covered by warranty though as batterys are normally consumables I think.