Here's a peculiar problem. I've recently acquired a second-hand iPod Nano 4GB. I can charge the battery with a charger that plugs into an electric socket, no problem there. However, if I use the datasync cable, connected to USB, it shows the charging icon. But the power just gets less and less. It starts 3/4 charged. Plug it into USB and a while later it's only half charged. Leave it a bit more and its in the red. I have tried several different USB sockets, and several different cables. They all do the same. I've also got several iPods, and this is the only one doing it. What could be causing this? Any idea how to stop it?