Use an opening tool to gently pry the battery up from the adhesive securing it to the outer case.

The adhesive is very strong. Work carefully and slowly, making sure to not slip and break any fragile components.

Use your thumb to pull the battery toward the left side of the Nano as you pry the battery's other edge out of the outer case.

From here, you can either splice the new battery wires or desolder and remove the old battery wires from the logic board entirely. These two options are detailed below.