Hey, I've been having an issue with my 3gs for a while and I cant find anyone who can fix it. The problem is that it always shuts down by itself and usually when it shuts down the screen will be blank usually there will also be darker verticle lines on the screen when the it shuts down, I cannot even switch my Iphone on because this always happens during boot but this NEVER happens when I have the Iphone plugged in via usb or wall charger it will work perfectly, I have been to a few phone repair shops and none of them were certain of the problem the first shop I went to said that it could be a problem with the LCD (which I doubt) the second said it could be the battery, battery circuits or CPU. I am just looking for a certain answer so if anyone can identify the problem please tell me. I am running IOS 5.1.1 (jailbroken) bb 05.13.04. Also I have tried downgrading my IOS to 4.1 but it didn't make a difference 
PLEASE help thank you...
PLEASE help thank you...