There is some information on the web that states the key fob port illustrated below charges the key fob. IT DOES NOT! It’s also stated in the Nissan Manual. It uses a 3V CR2032 that must be replaced as part of normal maintenance which is about every 2 years.

NOTE: The Intelligent Key port does not charge the Intelligent Key battery. If you see the low battery indicator, replace the battery as soon as possible. See Intelligent Key battery replacement in the Maintenance and do-it-yourself section.