Vostro 1000 Bum Battery

I've had my Vostro for about four months now, and the battery life on it is awful. I've set everything to the most efficient settings, yet it discharges within 30 minutes when on battery power. Anyone else having any problems like this? I've called Dell multiple times, and they say that because my battery isn't on the recall list they won't replace it, even though it's still under warranty.