Originally Posted by Dubdub
Have you allowed the battery to run down below 20% more than a few times? Lithium batteries do not like to be less than 20% and getting below that level more than 3 or 4 times can damage the battery. Sounds to me like that is your problem.
Buy an OEM battery from your carrier and see if that fixes the problem. Don't get a cheap knock-off however.
Actually the new one is OEM battery, and I tried my battery into another blackberry and it worked perfect!