Battery needs to be replaced will not hold charge.

This website does not actually provide repair services; however, there is a guide available to show you how to replace the battery here: Reemplazo del conjunto de la placa Lógica del iPod Nano 6ª Generación. That is the guide for a logic board replacement, but it will show you how to remove the battery in the guide. You can also purchase a new battery here: iPod nano (6th Gen) Battery.