The iPod Nano 7 isn’t the easiest to work with for many reasons. One issue seems to be that the battery pads on the motherboard are easily torn off when removing the battery.
I was lucky with this one in that’s it’s just the ground connector:
It’s the darker looking pad towards the top left. All you need to do is solder a jump wire to another ground point – I used a nearby screw:
Michael Webb's Blog 
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