iPod Nano 5th generation not charging?

I have a 5th generation iPod Nano and it is failing to charge fully. I have tried 2 different cords on both the computer and wall outlet. I've also tried holding down the middle button at the same time with the menu button (I've been making sure when I do this that it is in the "unhold" position).

It stays charged when it's plugged in but then when I unplug it, it still shows a low battery. What can I do? Thanks.