Take a look at Maximum Battery Life - BlackBerryFAQ
and this particular part:
2. Roughly every 30 charges, deliberately discharge your battery to 10-15%, and fully charge to 100% afterwards. This will help maintain the accuracy of the xxx8220;fuel gaugexxx8221; on the device (your battery meter or scale). It has nothing to do with the battery memory (as mentioned, Li-ion batteries do not have memory) but helps maintain the accuracy of the devicexxx8217;s percentage of battery charge left.
I don't do this, and I've never seen what you are seeing, but I can believe that sometimes the remaining life scale may need to be recalibrated. It isn't going to hurt to try.
If that doesn't do it, you could try another battery. But if it is still under warranty, I'd take it back to the place you purchased it and see about an exchange.