sounds odd. i have the same settings you have and get over a day with about 50% left with about 3.5 hours of usage. so great as compared to some, but solid nonetheless. perhaps go ask someone at an apple store about it, unless you hacked or unlocked it, then dont ...
but that is low as compared to mine. if you did hack it, make sure SSH is off if you installed the services app, as that helps out battery life quite a bit.