I need to replace the battery in my iPod nano 1st gen and 6th gen as well as two 4th gen iPod touches and one 5th gen iPod...

I need to replace the battery in my iPod nano 6th gen, my 30GB iPod video (5.5 gen), and an iPhone 6s. I may also need to...

Try using a iPad charger. I had this issue on a brand new pair of Studio 3’s, but after plugging it in to an iPad charging brick, it reached 100%. After battery calibration however, I would recommend trying to keep it between 40% and 80% charge unless you’re going on a long trip or something like that. You can calibrate most batteries by using the device until it’s battery is bellow 10% and charging it to 100% without interrupting it. So plug it in under 10% and don’t unplug it or use it until it is 100% charged. Because of your issue, I would recommend trying to use an iPad wall adapter to charge it to 100% if you attempt to calibrate it’s battery, however, I don’t know if this is bad for the device or the battery, and I would not recommend using an iPad charger every time you charge it.

Have you attempted a battery replacement? Also, is the battery 3rd party or does it have low health?