Replaced battery on dead iPod but now it wont charge

Hello, I had a dead ipod that when plugged in gave the error message with the triangle to charge it. So I replaced the battery and it came to life for a few minutes and i was able to view all the songs on the ipod and even connect it to my laptop. Since then it died again and went to white screen that said do not disconnect. I tunes kept telling me to restore the ipod but I don't want to lose my songs. I held down the menu botton and the centre botton and it came back to life. I can see all the songs but the battery will not charge. I put the original battery back in and and it still works but no charge-if i disconnect the battery it still shows no charge which is weird. the ipod only works when powered up via USB but if I connect to my computer it does not recognize it. Did I mess up this ipod? If so is there any way i can pull off all the songs off the harddrive or even put this hardrive into another ipod? Thanks in advance!