The Nikon EN-EL20 Rechargeable Li-ion Battery is a replacement or spare battery for the Nikon 1 J1 digital camera, and possible future Nikon cameras. The battery puts out 7.2V of power and has a capacity of 1020mAh. Lithium-ion batteries are long-lasting power sources that are immune from the horrible plague of memory effect, which kills a battery after repeated chargings.