Return to the device to BM?
Try letting the BB power cycle to about 10-15% a few days in a row (or 2-3 times in a row), and charging to a complete 100% each time.
After that, top off the battery any opportunity you get--ten minutes here and there during the day. This battery is meant to be topped off, not drained each cycle.
Maximum Battery Life - BlackBerryFAQ