Why does my replacing battery in iphone keep shutting down with battery?

So my replacing battery in iphone (3rd Gen Nano) is a little messed up. If the battery is half full or whatever, it just stops working sometimes. The screen turns pitch black. I think I;ve tried everything, charging it, pushing all these random buttons, and yeah. Im not much of a techie. This happens at least once a month. And it sometimes, after a week, turns back on. It;s really weird.Help? go to a service center.. the inside is probably messed up or short-circuited.. have it checked out

Is there any way I can transfer purchased apps from my Iphone 4 to the computer?

My Iphone (4) is pretty much full of apps and to clear some memory I want to put some apps on my computer (it;s not an apple computer). I have downloaded itunes. Is this possible?If so How would I do this?I don;t want to delete them as I paid for them and I still may want to use them in the future. The applications can be synchronized to your computer if you have connected your iPhone 4. But if you got media files (images, songs and movies, etc), you can try this simple tool which may help to b