PCB target voltage reading too low on Atmel ICE Programmer
It seems like you have used altium for you circuit. 
Usually the designators are used as numbers and the description of the pins is the description. As you currently did it, it is unclear wheter it is a net name or the designator of the pin. 

Assuming from your comments, it is the pin designator, in which case you forgot to connect the ground of the battery to the rest of the circuit. As well as one of the ground pins of your microcontroller.



As a reference for you next circuit, this is the conventional way in altium to make your pin designators: It helps preventing confusion between net labels and pin designators.