Battery Replaced, Recognized by Computer, Won't Charge?
I just replaced the battery with an iFixit (super easy!) and the iPod started right up. It is showing little to no battery power. When I connect it to by Macbook, iTunes recognizes it, but it does not charge. I’ve tried multiple chargers with the 30-pin cable (brand new) and I can’t get the lightning bolt to come up.
Your problem is the connection. The iPod 3rd Gen does not charge through USB but needs Firewire connection. This model only syncs through USB. Hope this helps, good luck.