Are you using a theme? Some do not portray the battery remaining as it should. Lithium batteries do not need to be power cycled as the old NiCads required. In fact, lithium batteriesy seem to perform, better when kept topped up. Letting them run down below 20% on a regular basis can damage the battery. I always keep mine plugged in when in the office or car for an extended period.
Also, this from our FAQ may help: Maximum Battery Life - BlackBerryFAQ