BB Bold :: 9900 Not Powering On And X Mark On Battery

I have a Bold 9900 which I just bought 3 months ago. It has been fine over the last 2 months however the last month its been giving a lot of problems. While I was using it the screen went black and I tried to restart it (power back on and taking out the battery and sticking it back it) but the red led light would come on and it would not power up. After sticking it on the charger the red light would come on for 1 minute, then the battery sign would show saying that it is charging but after 1 minute, it would show a red X mark on the battery symbol and it would not power on. I have gone through this process 2 times (I have bought 2 JM1 batteries for the device from blackberry) however it still gives the same problem. I sent it to a phone repair shop and they gave it a try. They say that the batteries are fine, but the blackberry is not able to hold in the charge and has a problem with charging it.