This a 26650 Polymer Lithium Ion Rechargeable Battery - 3.7V 5000mAh
These round high capacity cells have been mainly used in flashlight type applications but with the capability to be used as a drop-in rechargable cell at 3.7V with a current of 5000mAh. This is a great battery option for those of you who need a simple to install and replace cell with a lot of juice.
These are high quality generic 26650 batteries. The image is for illustrative purposes only.