Nikon has issued a service notice for the EN-EL15 Li-ion Battery:
This is an important announcement regarding the EN-EL15 battery which is used in the Nikon D7000, D800, D800E and Nikon 1 V1 cameras.
While Nikon takes great measures to assure high quality products, it has come to our attention that a certain number of EN-EL15 batteries manufactured by one of our suppliers did not meet Nikon’s internal quality standards. In extremely rare cases, this may cause the battery to overheat and the exterior casing to become deformed. Batteries exhibiting this problem have only been confirmed in the Nikon manufacturing process. We have received no reports of this problem from the market. Therefore, in order to ensure the safety of our customers and their equipment, we have initiated a voluntary replacement scheme for applicable products.
Customers using an applicable EN-EL15 battery may request a replacement battery ...
If you have any Nikon EN-EL15 Li-ion Batteries, you need to read the rest of the service notice here to find out if any of your batteries are included in the recall.