Hello L, I'm sorry for the inconvenience that you have faced with your NUC. I’m not sure why you got a defective battery.
In regards to the replacement of product, it will be necessary to replace the whole NUC, since we don't have spare parts.
Please contact the place of purchase. If for any reason they do not want to replace the unit, please get in touch with our Warranty department so they can help you. http://www.intel.com/p/en_US/support/contactsupport
Thank you very much for your answer. I contact my place of purchase.