The Nikon EN-EL14a is a compact rechargeable battery for powering compatible camera equipment. Nikon identifies this item by SKU VFB11408 and describes it as a lithium-ion battery, making its purpose clear for photographers who need a rechargeable power source in a small format.
Nikon characterises the EN-EL14a as high capacity and intended for long operating life. It can serve as the battery in a camera or as an additional charged battery for a photography session, helping keep a camera supplied with power for longer between charging opportunities. The confirmed details here are its rechargeable lithium-ion design, compact form and capacity description.