As posted above the batterys can drain fast with an App that is constantly looking for data. The other thing may be the area your in. If the cell serivce is bad the radio on the phone keeps looking and that will drain the battery fast.
As fourstringfuror said make sure you do type a branded OEM Blackberry battery if you decide to get a new one.
Another bad boy is the use of bluetooth data. Another is letting the battery discharge below 20%. LI batterys do not recover but show full charge and when they get to about 45 to 50% they drop to 0% quick.
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